>>58080394Goh needed to learn a lesson in humility. He was a self proclaimed smart guy who didn't know shit about collaborating, making quick decisions, or taking orders. Gary was unironically a perfect match for Goh, as they both catch a lot of Pokemon and have aspirations to do with Pokemon biology, and Goh's difficult personality allowed Gary's shithead bully side to re-emerge, which is when he's at his most entertaining.
If Gary went up against Ash it'd be boring, because their dynamic is already resolved and Ash is no longer the type to get baited or instigated into a fight. Gary and Goh had a great dynamic, the show just failed to put more episodes into it.