Class capstones vary so utterly in power it's kinda ridiculous. Paladins get a subclass specific cool button to smash, clerics get to guarantee their Divine Inspiration, artificer gets a passive +6 to all saves, barbarians get unlimited rages and +4 str/con, bards get...one BI dice, if they roll initiative and didn't have any left.
Sorcerer and Warlock are definitely on the lower end of impressive for capstones.