Why does Adaptive Helm exist really?

MR item that reduces subsequent incoming dps from duplicate sources. Counters DoTs via 1 item. The combined MR and HP means it double-counters mages, literally forcing mages to cast the spells again to reliably dps. (Health hits mages pretty reliably hard. A 200 damage spell sounds powerful, but 300 health still means you gotta cast multiple times to overcome it and base health.)

Also has some health regen and CDR for reasons.

(Hello Liandry's, you worked so well against health, you'll now work worse... in junction with MR that surpasses your magic pen.)