No item punishes an entire class of champions as hard as adaptive helm punishes sustain mages
? It doesn't punish tanks for being tanks, only for building excessively tanky so they don't become completely unkillable. I mean Sion might be punished by it even without building super tanky because of natural HP gains but that's about it.
? Nope because
exists and can mitigate a lot of grievous wounds effects.
Counters everything and the only things sustain and DoT mages can do in the game effectively with only 1 item purchase and since it's % based it will scale up and mitigate even more damage regardless of how much AP you stack as a mage. It is essentially a 1 item wonder if the enemy team has a Malzahar, Ryze, Cassiopeia, Kassadin, Taliyah etc because it mitigates so much damage by itself without the need for further MR.
counters AA-reliant champions
counters all immobile champions
counters assassins as AD champions
counters assassins as AP champions
and its variants counter all things tank
counters all things tank