Earlier in the chatbawks we had a conversation going about how effective a GKT 'Thunderbubble' could be. Let's take a look at these two units within this construct then and see how it plays out. This post will focus on two things. The strengths, weaknesses and ultimate differences between GKT and TH/SS Terminators and how they interact and support with the army built around them. This latter part is important in determining the effectiveness of the list whilst the former is more of a comparison of units.
TH/SS Terminators
This is the gold standard of raw efficiency and pure combat oomph. Everything gets compared to them and is generally found wanting but there are two major weaknesses of this unit which are often overlooked. First they get swamped in combat easily. 2+/3++ can go really far and in Blood Angel armys, 2+/3++/FNP goes even further but they only produce two attacks each, three on the charge. They strike last. TH/SS Terminators are not horde control devices and this is one of the best ways to deal with them. Chuck a bunch of wounds at them either via shooting or combat and they will fold. This is exemplified by the second major weakness of the unit. They have no shooting which reduces their threat range significantly. This means you either need to shell out more points to increase this (i.e. Land Raiders, Stormravens, etc.) or work them in on foot (which is what Thunderbubble does).
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That being said TH/SS Terminators are hyper point efficient. If you are able to enact their primary role (combat against non-hordes), they kick ass. It's impossible to create such a durable and offensively potent unit without paying way more points. Look at Vanguard, Command/Honor Squads, Wolf Guard, etc. Starting slapping on Storm Shields + combat weapons and you're looking at 60+ points per model and often without Terminator Armor. TH/SS are ultimately the definition of a rock or super unit. They can take damage and deal it back out but they are not without their flaws and are not a 'do it all' unit.
Grey Knight Terminators
A lot has been made out over the extra expense one pays for power armored Grey Knights compared to other Marine armies and how this affects their play on the tabletop. Not so for GKT who have the exact same statline compared to Shootynators but with the Grey Knight associated buffs compared to other armies (i.e. combat tactics, red thirst, Fearless, etc.). The issue for GKT becomes they aren't bringing as much uniqueness to the table as other Shootynators who bring stormbolters and mobile heavy weapons. The rest of the Grey Knight army already has this so the question becomes what benefit do you gain in using GKT over power armored Grey Knights?
In terms of having relentless for Psycannons the point efficiency is basically the same compared to Strike Squads on the move and less so when stationary (i.e. keep moving with the Terminators) so there is no real mathematical gain in shooting. What GKT ultimately bring is better combat ability and on a platform which is happier to go into combat for Grey Knights. They still aren't a super good combat unit like TH/SS but are more capable than their power armored counterparts due to invulnerable saves (and thus gaining a benefit from swords) and point efficient halberds and hammers.
This boils down to the following: GKT are the generalist Terminator. They have effective shooting, pretty decent defenses and good combat ability. The best thing about their combat is the options a unit has. With free swords (4++), halberds (I6) or hammers (S8-10) and depending how falchions are FAQ'd (5 points for +2A = very nice), GKT can be equipped to handle anything and everything with upgrades like Brotherhood Banner and Psybolt ammo very good on large units and increasing their potential in both shooting and combat.
TH/SS in Thunderbubble
Your standard Thunderbubble list isn't fantastic. It's a good list with solid options and is hell against certain opponents (i.e. elite assault based armies) but the major divergence in roles between the TH/SS and the rest of the army means most combat armies will out-combat you and most shooting armies will out-shoot you. This seems pretty black and white and counter intuitive as Marine armies are often more generalist than not so we'd expect this to happen and thus the Marine army needs to combine their combat and shooting abilities to win. With Thunderbubble however the TH/SS weaknesses are exposed. Against shooting lists the TH/SS are slow (which is why Gate of Infinity can be really important) and since they have no shooting options, they aren't going to impact significantly impact the game quickly. This gives the shooting army time to suppress the shooting aspect of the Marine list and deal with/delay the TH/SS themselves. Against combat armies with lots of bodies, there's nothing to support the TH/SS which makes them very vulnerable and not point efficient.
That being said the TH/SS are still a scary prospect for anyone to encounter. If they reach the lines of shooting armies, they will cause a lot of damage and they will take firepower away from the rest of the Marine list. Combat armies are going to have to go through them and whilst they are expensive and inefficient against hordes, they are going to slow the tide and allow the Marine army to re-mobilise and deal with threats appropriately. Although TH/SS have some major drawbacks which are exemplified in the wrong match-ups with this type of list, they do still have advantages for being run this way. The army is far less reliant of cover for example since that 3++ is constant. This offers up a lot more opportunity for the Marine army to take advantage of terrain and generate clear firing lanes whilst not disadvantaging themselves. TH/SS are also capable of combat squadding effectively (if you buy large squads of GKT w/banner, you shouldn't combat squad) which can greatly increase their effectiveness against combat armies as they can delay for longer and not get pulled out of the way by an intelligent opponent (let's assume all of our opponents are intelligent btw).
Ultimately the Thunderbubble list is a good list but the weaknesses of TH/SS Terminators are often at their highest in these lists in particular match-ups. This leads to the list not being as good as it could be whilst still being good.
Grey Knight Terminators in ...Psybubble?
What a stupid name... GKT play a much different role compared to TH/SS in this army as they are far less fearsome in combat but have a lot more support (Nemesis Force Weapons...ho!) and aren't hopelessly useless against hordes. Importantly they are not inefficient against lots of lists and whilst they are not as effective as TH/SS at taking damage or dealing with elite armies (unless they can wipe out squads with I6 halberds), they are more effective across multiple match-ups which comes from their generalist nature. GKT are quite effective whilst not in combat thanks to their shooting which allows them to impact the game not just as a defensive screen, but as an offensive threat as well. This will often fit in with most Grey Knight armies as well since GKT are based on the same premise as most Grey Knight units (storm bolter + force weapon).
Furthermore, the damage resistance and damage potential of the GKT can be greatly improved with a Librarian thanks to the powers of Sanctuary, Shrouding, Quicksilver and Might of Titan; all of which can be cast in the same turn. Although this still doesn't make the GKT as durable in combat (with only a potential 4++), it can greatly improve their survivability to shooting and decreases the amount of attacks the GKT might face by defending against charges (sanctuary) and allowing the GKT to do more damage before hand (Quicksilver and Might in their own turn + of course Hammerhand). The big problem with shrouding of course is generating the original 4+ cover on the GKT. This isn't too hard with 5th edition rules but limits the application of this screening unit and may often expose other units in the process. These abilities are also all psychic powers so are subject to psychic defenses.
That being said, the Terminator-wrap is far less needed for the Grey Knights army regardless. Although the GKT themselves seem to fit the roll better, particularly with a Librarian's buffing ability, the Grey Knight army is midfield oriented. Whilst they can obviously gain from having a dedicated unit to be used in combat and to screen against assaults/shooting, the enemy is going to be more capable of getting around this unit and engaging other aspects of the army. This is heightened by the points you have to sink into this unit (100 more than TH/SS Terminators + a more expensive Librarian) and the loss of ability to effectively combat squad. The unit can be cheaper without a banner and therefore effectively combat squad but then the unit(s) are much less scary in combat.
There is of course the lovely character of Mordak to consider who removes the reliance on the Librarian for 3+ cover saves thanks to Ghost Knights. Whilst Ghost Knights don't have as many options as regular GKT (i.e. psycannons, though a TDA inquisitor can be attached), the unit can expand due to Mordak's special ability, comes with Stealth for free and has the ability to deepstrike accurately on T1. This is much more of a dedicated wrap since the unit has less shooting ability but importantly comes with stealth and can get into a very aggressive position T1 thanks to accurate first turn deep striking.
Conclusion
Ultimately the GKT are probably a better unit as an actual wrap due to their combination of durability, combat prowess and shooting ability. TH/SS are far more durable across all situations and much more deadly in combat in the right circumstances but their major weaknesses, hordes and lack of shooting, are exposed in the Thunderbubble list. That being said, most Grey Knight lists aren't going to benefit from having a combat unit as a screen compared to other Marine variants due to their midfield nature. Whilst the GKT are effective in this role, the opponent has more opportunity to circumnavigate them and focus on the rest of the army. A Grey Knight list could be designed around this unit with a more backfield nature (henchmen in LasPlas RBacks + Psyfledreads) but that's not playing into the strengths of the codex.
In the end GKT will generally fit quite well into any Grey Knights list due to the nature of how Grey Knight mech works (essentially hybrid). Although they can fulfil the screening role of 'Thunderbubble' in the right circumstances, there are a lot more options for them. TH/SS on foot however are designed for this and whilst ultimately weaker at it due to their limitations, make a better 'Thunderbubble' army. This army still has it's limitations as discussed above.
