I agree, Stan was left in the ditches comparing to others characters. Maybe having him as a shut-in dweeb did not bring enough opportunities to flesh out his character.It can work its just the whole thing feels like it got scopecrept as is so making it work would be too much work not enough payoff. But yeah he feels kind of redundant, like a male Holly could had been interesting had we been given more earlier, by now it is somewhat pointless. Holly is female so her glow-up does not need to be as drastic to get results but her training montage arc was wayyy the fuck earlier.
He could shine in the OF route, but even there his content is limited. He acts way too late in the story imo.