Managed to fix it.
Both .glb and .fbx had bones offset at odd angles (30°, 60°, 105°,etc), and .fbx also had extra bones at the end of every bone
.psk imported with the bones offset by 90° (the official blender extension site has a .psk importer)
Went in and manually fixed the offsets everywhere, and now I've got a working rigged model again.