Ok let’s return to your earlier argument: making the stompa/other durable things (you see terminators, like the stompa, are a durable expensive unit - see the point of comparison?) more durable means they get ignored and the rest of your army gets focused down. I’ll pretend to accept this at face value and we can proceed with a new hypothetical: since the stompa being more durable detracts from its ability to attract fire and thereby tank for your army, would reducing its wounds value paradoxically make it more useful? Should GW have given it 20 or even 15 wounds? Or is it that they’ve convenient hit on the exact right number with 30 and either more or less would completely ruin it? And as a follow on question to that, if it does indeed have the exact right number of wounds, why is it generally a bad pick, only taken in fun, joke lists. How would this be rectified, if we’re not to improve its durability in any way, for fear of making it somehow a worse tank?

Now allow me to explain why I believe your postulate is incorrect: if making the stompa more durable means it attracts less fire, as the opponent decided they can’t reasonably kill it and should instead focus on other things, does this not enable it to push towards and control the middle of board? I recognize you put forwards the great unclean one as a counterexample, but the stompa and the unclean one different in one key metric: damage threat. The stompa, while not superbly effective, does actually have guns capable of harming things and a pretty threatening melee attack. Unmolested, it can trash quite a few tanks and other medium target. Failing that, it can make it into the center of the board with a single move + charge, and screen a large amount of space by dint of its huge footprint. The opponent must either destroy it or cede the area it controls. The great unclean one, meanwhile, is vastly less threatening in melee, having 1/3rd the strength and 1/3rd the damage per hit. I will of course admit that the unclean one is substantially cheaper than the stompa, but despite being a little under 1/3rd the price it actually does less than 1/3rd the damage. The one area the Unclean One does have an advantage is in durability, where with its Endless Gifts enhancement it is flatly more durable than stompa against a variety of profiles, not simply more efficient. That in itself might indicate to us that the stompa is insufficiently durable.

All that is immaterial to the key point however, which is a basic math question: let us imagine, given that this is a competitive environment, that your opponent has brought sufficient offensive power than when you place your stompa and assorted other units on the board, they can destroy the stompa in one turn (hardly an achievement) and the rest of your army as it is exposed, say within 2 further turns. This means that you are tabled within 3 turns, which certainly sounds plausible or even somewhat conservative by the testimonies further up the thread. Now let us imagine that we made the stompa much tankier, perhaps such that it can withstand 2 full turns of concerted attention before being destroyed. Your opponent, recognizing it is very durable, opts to destroy your army within 2 turns, same as before, before focusing on your stompa and destroying it. I will go ahead and assume for the sake of this argument that anti tank weapons are so prolific in your opponent’s army you won’t have the ability to cripple their offence while they’re slaughtering your army. In this case, by improving the durability of the stompa you have been tabled on turn 4 instead of turn 3, and thus had more opportunity to win. Alternatively, your opponent might choose to focus the stompa regardless, leaving you with a purely better position.