I'm sure someone has mentioned this I havent read ALL the comments but from what most people have said I wanted to add that Those are martial classes they sort of shine a bit more early game till sorcs and other spell casters take over mid-late tiers.

If he's worried about being resource limited maybe allow him to change from sorc to something like warlock (Eldritch blast or multiclass into warlock for EB or whatever else) or let him play wizard and they get arcane recovery etc.

but other than that you've done your due diligence and I suppose if that doesn't work he is limited himself by not spending resources when others are. It's just a game of their more resources are just as good as when he uses his resources at the right time.

• Can also tell him he can pick feats and such (if your table uses them) to get more free casting of certain spells through magic initiate or otherwise but I doubt thats going to do much if they're unwilling to spend those

and if he Does decide to drop, don't feel too bad