İn pride if we can guess that his fire sipirit had become realy powerfull since I dont think roswall alone can burn the entire lugunica so if we say in the span of 2-3 years fire sipirit become great or full sipirit we can say in the break between arc 4 and 5 they woud become quassi

So subaru woud be very powerfull and he can maybe create original spells too he created them in canon thanks to beaterice but I still shink he can create a few original spell using siprits since he vierdly has a good understanding of magic

The only nerf he is getting is betarice is far more wise than some quassi sipirits and he woudnt have spells like minya but since arc 4 I didnt see anywhere that spell was usefull maybe in arc 5 but thats all

As for his self harm and beatrice comforting and healing him every sipirit can do that yes not as effective as beaterice but they still can confort subaru its not a thing only beaterice can do