All monsters have terribly underbalanced armor compared to player. Player armor is about 5 times as good as the monster equivalent. This is partly because monster armor is always 100% coverage on all body parts, but also because it didn’t get rebalanced for a long while, while player armor gets buffs all the time.
Look at soldier zed: it’s like 8/16 and can be easily punched to death. Tankbot can be killed by throwing steel chunks at it (it could use a big armor buff, now that you can easily run from it).
At 24/30, the only thing stopping the players from wrecking those with planks or sticks would be their special attacks. If you want to make it actually feel armored, you’re looking for values like 60/60.
At 60/60 it would still be easily killable by competent fighters (easily means “just attack”), while the weaker ones would require special tactics like using fire, spitter acid or point-blank shotgun/rifle blasts.
If you wanted it to feel like “power armored monstrosity oh god how am I going to stop this thing”, 120/200 wouldn’t be enough without traits like fire/acid/etc. resistance. It would still be way easier to kill than shoggoth.
As for mechanics: you can make it immune to fire (flames, not gunfire) by making its material steel rather than flesh. Making it acidproof would prevent easy cheesing. Player power armor melts in acid really quickly, but monster items don’t melt in acid until they spawn, meaning it would be cheesy to allow turning power armor zeds into loot pinatas with acid.
Giving it immunity to stun would be helpful (it’s not currently coded, but it would be a useful flag), otherwise any player attack capable of damaging it will also stun it.
