Chocolate salty stars.

Deathstar.

The name itself is enough to make people laugh these days. In the olden days, the term was used to refer to ultimate bricks (4th edition marine command squads, with three characters), killing machines that, realistically, just couldn't be stopped (nob bikerz), and other assorted stupidity. "Like?" Early 5th, three ironclad dreads.
Yeah, we've come a long way since.

The key thing behind 'deatstars' is points-denial. If you can't kill it, you won't get the points, yes? So if we're playing killpoints, and I have three 500 points units, versus your 1500 point army, that's magically given me an advantage, right? Maybe? Kinda?
No.

In a game like fantasy, where you can easily stack defensive buffs/stats, and few - if any - armies have the tools needed to assail your deathstar, sure. Then 8th hit, and we got purple sun - which is a type of neutron star. I see your Purple Sun and raise you a Banner of the World Dragon. I see your banner, and raise you laserguided, knightly trebuchets. I concede.

Deathstar's don't work.
Their lack of usefulness in 40k is such that even warseer understands this, yet a new class of super-unit was invented to take its place: the mini-star.
Variously known as 'mini-stars,' 'dwarf stars,' 'white dwarves,' and 'huge wastes of points,' these units focus on killiness and durability - rather than outright denial.

To volunteer for star duty, you must be elite infantry. Monster, bike, footslogging terminators - it doesn't matter. If you can't make use of wound allocation, you're automatically disqualified.
Here, two examples.

5 paladins: apothecary, 2 master-crafted psycannons, 2 master-crafted hammers, 3 master-crafted halberds - 425

Layout: Apothecary, halberd.
Psycannon, hammer.
Psycannon, halberd.
Hammer.
Halberd.


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5 nob bikers: painboy, 3 powerklaws, big choppa, cybork bodies, boss pole, waagh banner - 380

Layout: Painboy.
Big choppa.
Powerklaw, waagh banner.
Powerklaw, boss pole.
Powerklaw.

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Paladins obviously have a shooting advantage. One large blast, two stormbolters, and two psycannons is a lot more dangerous and useful than 5 dakkagunz.

Durability?
Terminator armor is miles ahead of T5 with carapace equivalent, to a point that we'll get to after this waffling. Both units have feel no pain, must suffer ten wounds before killyness decreases, and have the same invulnerable save. Of course, there's the very real difference that battlecannons nuke the nobz, but barely scratch the terminators - however, battlecannons are terrible, so never taken since 4th edition ended. It's worth noting that T5 is as good defense against S3 firepower as 2+ armor save, by virtue of shifting the t0-wound roll far into the stratosphere.

The kicker then isn't the battlecannon (since it's never taken) - rather, that demolisher cannons destroy both, while the net durability against regular anti-elite infantry firepower (meltaguns, lascannons, lances) is pretty much the same. In fact, your terminators are so immune to small-arms, no one is ever gonna shoot them, other than as acts of defiance, and this virtual immunity will more often than not only come into play once you tie up some infantry.

In combat, the nobs are dramatically worse.
Yes, they have three powerfists, with strength 9 on the charge, and blah blah blah, but they're striking last, can't drive into terrain without risking damage, and 4+ is terrible for a combat unit - even if it has feel no pain. At least you're T5 to soak up some basic attacks.
Almost everything the paladins get the drop on gets speared 300-style, and survivors are flattened by S8/10 master-crafted hammers. Multi-wound targets? Okay, so initiative 6 force weapons. You more often than not die. Immune to that, too, somehow (avatar) Force hammer'd.
Against armored targets, the nobz ARE better. 12 fist attacks at S9 brings them as close as it gets to orkish reliability, and the 4 S7 aren't that bad, either, but when was the last time you got the drop on a stationary parking lot? It happens, but isn't something to rely on.

The nobz do have a not insignificant points-advantage, but this is more likely to reflect in the army having more guys, rather than the orks adding another nob. You know, because overkill tends to accomplish nothing.

Obviously, bike wheels move a lot faster than terminator'd feet, but with two master-crafted psycannons, and the ability to deep strike, the terminators aren't exactly in a hurry to pimpslap people. 18 threat range is something you can't overlook, however. It's nice to have the reach to grab most units.

However, all the above is just numbers.
Numbers are lots of fun, but they fall apart when you bring them to the table. Essentially, nobz and paladins are little hammers that cost ungodly amounts of points, yet produce huge numbers.
You really can't argue with the effects of a hammerblow, but what if it misses? What if it's a glasshammer? What if it's moving really, really fast, but even that speed's not fast enough? In either case, one must consider things outside the numbers.

Paladins, like all terminators, can be deepstruck in. Not only can you teleport them, but the book they're from lets you augment them with these handy spells, special abilities that can't be countered (grand strategy), load them in behemoth transports that aren't 50 foot long, with open topped armor 12 sides...
Because paladins are modern, they can be given heavy weapons, have magic powers of their own, their default implements can be given re-rolls, kill things instantly without necessarily striking last, and you can even split a full unit of them into two smaller ones. Natural weaponskill 5, initiative 6 weapons, and S10 attacks all help, too.

Nobz get re-rolls for morale tests. That's it.
They don't have built-in defense against psykers, or add heavy weapons fire to their army. The combination of low model count and bad leadership often renders nobz impotent before they even get to bring the pain, so bikerbosses are very likely to babysit them - a true deathstar of inflexible excess.

Yes, the boss detaches when the mess on wheels is close enough, but what if the nobz had the leadership to operate on their own, so the boss could be someplace else?
When all's said and done, blowing 425 points on one unit may not be the smartest thing, but it's miles head of 380 points for another that can only do one thing, and still needs babysitting to get there.

No matter how you twist and turn, 'stars' are always gonna be a terrible to 'fun' concept, but some represent better value than others, largely because they form part of their army, and so won't be an army in your army, still relying on other components for support.
The paladins above ARE their own support, and a fully functional element of a 5th edition army. Excessive cost, yes. Excessively killy? Also yes. Value for the points? Low to moderate.

Moar expensive isn't always moar betterer.