The issue in this case being Larian's very, very poor decision to only have one skill vendor in the act who sells Pyro, Geo, Hydro, Aero and Poly skills.
The issue being that since the final fight of the game uses different rules, I wanted to change my skill setup to take advantage of those and use skills I'd otherwise never bother with. Except now I can't unless I'm willing to go back a few hours and redo a bunch of stuff - which I am not.
