Fairly often in a discussion, it seems I'll get into this little argument:
ME: "Assault Marines/Grey Hunters/Berserkers just aren't all that great in combat, so they need to have other tools."
PERSON: "WTF? They're great combat units, they have XX attacks on the charge and blah blah etc etc."
ME: "Yeah, but a real combat unit will roll them over, so you can't rely on assaulting things to solve your problems."
PERSON: "What do you mean a 'real combat unit'? They ARE a real combat unit!"
ME: "Not compared to something like a monstrous creature, or Thunder Hammer Terminators, or stuff like that."
PERSON: "Oh, sure, if you compare them to THOSE they lose, but against anything else they'll win!"
I'd like to set this straight: if your unit can only beat things that aren't designed for combat, you aren't a combat unit. You are, at best, a generalist, and maybe it means you're just bad. However, I think this also comes partly out of a lack of clarity of what I (or they) mean when terms like "real combat unit" get tossed around, so let's have a little discussion time.
As I see it, there are basically four tiers of combat ability in the game. Of course, the difference is actually more subtle than that, but grossly speaking, we can group most units into one of four categories:
Bad combat units are just that: bad in a fight. You will very rarely charge them into combat intentionally and usually only dire circumstances. This mainly includes shooting units/armies like Guardsmen, Tau of all sorts, etc.
Mediocre units are mostly things with MEQ-type statlines and no real special gear/abilities that help them out- Tactical Marines are a classic example here. They can tie up some units for a while and inflict a bit of damage if you get lucky (or paid what is probably too many points for an upgrade), but for the most part combat is, at best, a distant second or third strategy for them.
Acceptable combat units are those that are actually designed, at least to a degree, to get into a fight. Some, like Assault Marines or Berzerkers, are just MEQs with a bit more hitting power; others rely on special rules, army-wide abilities, or a superior statline to do their thing. The important part of this equation, however, is that while such units may be reasonably strong in a fight, they can't compare to full-on dedicated combat units or are only situationally strong (such as relying on getting the charge, etc.) Grey Hunters, Grey Knights, and Ork Boyz all fall into this category due to their individual weaknesses; significant vulnerability to one or more melee strategies tends to be a defining feature of this level.
Good units are the best of the best; they at least stand a chance against most of the other hardcore melee units in the game, though of course there is an element of rock/paper/scissors here as the various strategies line up against each other. These units virtually always have attacks that ignore armor and usually have an invulnerable save of their own to ward off such attacks. TH/SS is the prototypical unit here, but Whip/Sword Warriors, Nobz, Paladins, TWC, etc, all have their places.
Of course, being pretty broad categories, there are plenty of units that slip through the cracks, but conceptually, this is how I tend to rank things. Either you are a specialist who is good at their job, a generalist who can handle themselves, Joe Average, or Sucky von McSuckington.
The tricky part is now translating these into tabletop usefulness. Grey Hunters and Grey Knights Strike Squads, for example, are both acceptable combat units, but their other virtues (AT weaponry and general shooting, good transports, scoring status) make them very viable choices. Berzerkers, on the other hand, are an acceptable combat unit that has no other effective roles or tools and thus ends up being rather unimpressive. By the same token, not all good combat units are created equal- Sanguinary Guard, for example, have no invulnerable and thus will tend to roll over and die to any other unit in the category, but will slaughter most things below their tier. Kirby often calls these beater units as they very effective at dealing with certain unit types but can disappear in a flash against good combat units. Similarly, a Tyrantstar is effective, but lacks mobility options and is very resource-intensive.
Basically, when you're looking at what is and isn't good in combat, you need to keep the opposition in mind. If you aren't one of the big kids on the block, you really can't afford to be devoting yourself wholesale to fights you aren't going to win.
