I never had the "problem" of being over leveled in any of the games I ever played. If my opponents were ever lower leveled than me, I saw it as a good opportunity to start using other party members. I would even often get bored of my current party, or if I saw something on a new route I liked I would just pick it up and start using it instead. I sometimes boxed my starter after fully evolving it after the 5th gym or so. Not necessarily anything against my starter, but simply because by that point I had found a lot of other pokemon that I wanted to try using instead. Is your starter really the only guy you encountered in your whole journey that you liked? I feel like you are being deliberately disingenuous. I mean sure, the games are easy no matter what. But that's a good thing, because it allows you to use just about anything and be successful. I'm not trying to larp as a speedrunner.