About what I talked about the slog that ch 5/6 would be in PF2E or D&D 5E, one spell :
Finger of Death - It is save or die originally, in the 2E, in 3E and PF1e nerfed to only deal a very high amount of damage, so even at lv 20, the maximum damage is 200. In Generic wow clone : tabletop edition it got heavily nerfed and the nerf was carried to 5E and PF2e. Dealing mere 70 damage on PF2e and mere 60.5 average damage(7d8+30) in 5E. In both games, you can find low CR mobs with 3 digit hp(something that even in Dragons was rare in 2E).
Even DDO which is a mmo, where you expect to see way more balance BS, FoD OHK stuff. I know cuz I have a lv 27 Pale Master there. A lot of mobs have protections, so I need to cast disjunction before attempting to finger then.
Phantasmal Killer is described as "emotion, fear, mind-affecting". Which exactly immunity you're writing about? And what other weaknesses this foe has?
Yep. You can kill even spawn of rovagug with it. Undeads, I believe that some undeads and constructs are immune to it but that is it. Illusion magic suffers way less restriction in OHKilling capabilities than necromancy in 3E.