So, i forgot to post what happened lolAite, i'll try that probably tomorrow and post the progress, tyvm J-man from an Easter play <3
Basically erased game save, uninstalled smash via data management, did the fix bit thing and installed xenoblade remastered and it ran fine.
And then, before doing the sd card tests, wanted to make absolutelly sure it wasnt bad luck 5x in a row downloading smash, so i searched online for a .nsp checker and found Nsc builder (cant link yet), which told me the nsp was indeed corrupted, somehow.
Maybe its my pc doing weird stuff during decompression, but oh well, posting this story for posterity. I went to borrow a smash cart from a friend and dumped it and it runs fine.