I've seen nearly all of the episodes and I don't see what he does that's so stupid most of the time (almost at the Sinnoh league). Aside from the "My Pokemon get stronger because I believe in them" crap, of course.
He wants to win and become the best, doesn't he? So why would he leave his best Pokemon behind / not use them when he needs them? Aside from Pikachu and the odd time when he goes and gets his Sceptile or something.
I know it's for the sake of continuing the series... but it's just a little weird is all.
The Official Luigi of the Super Smash Bros. Wii U Boards