People don't use it because it has a reputation for being broken, and not stacking with veterancy bonusses. However, that was (stealth) fixed by Mr.Smith a few patches ago.
To be honest i saw few top20 players using this ability even when they didnt have any vehicles near their infantry, its such a situational and badly designed ability that i cant see anyone taking it over skill planes or self smoke.
I think more hitpoints in exchange for armor is definitely a buff.
With the way armor and penetration works in this game, armor is not very reliable at all, and especially not the "medium-heavy" category of the 300s. The average anti-tank gun can penetrate (~66% chance) 5 times in a row or it can bounce 5 times in a row. There is so much RNG involved, it's almost impossible to make a sensible estimation on a situation.
Health however, is much more reliable. You know exactly in how many penetrating shots it can go down, that's a fact, there's no RNG that can change that. Now you know most shots will penetrate, but you know exactly how many the tank can take. This means it's much easier to judge chances and risks. The armor for health change was done for the Panthers about a year ago and it has made them much better to play both with and against, because there is now less RNG involved and it has made it generally much easier for either side to judge whether a push or a chase is worth it.
I would personally definitely count this as a net survivability buff. Especially for team games, where AT is usually concentrated and in abundance, and in which a higher health pool is a lot more useful.
Well you said it yourself. You may survive last shot thanks to more HP or you will eat every shot, because that 30 armor was all you needed to bounce, and pershing is dead. Its adjustement not straight buff.
I don't think it's a nerf at all. It still (on average) kills clumped up squads in 2 shots. The rare oneshots are gone, but now it will hit more often and deal more damage against squads in the open.
Its certainly a nerf in the case of pershing as one shot wipes was what this tank was all about. Pershing missing hits on infantry wasnt really a thing so this buff is pretty meaningless. It was a good change to make wipes less common but less wipe potential combined with slower reload is overkill without compensation. +5 range on vet2 is whats missing.