As someone who cleared Abyssos Savage:

P9 wasn't too bad but lag will 100% kill you, P10 is 90% your party members killing you because of tethers, P11 is super easy on mobile classes, difficult on turret classes.

P12 I'll admit is pretty spicy though. The boss hits like a truck, party members will absolutely kill you with tethers, particle effects often obscure key mechanics that can kill several people if not respected. Definitely harder than P1S.