>>18184562If you discount BW, which was a huge mistake, Ash did improve. He was offered a position as a Frontier brain in advanced generation and then made it to the semi-finals of the Sinnoh league. He went into Kalos a seasoned trainer and it reflects in how he fights, trains his pokemon and learns from battles. Of course he still faces challenges because 1. power levels aren't linear like in the games, which are simplified, and 2. what the fuck is the point of watching a show where the character just beasts through everything? Conflict and struggle makes things interesting.
If all the episodes in the show are one day, give or take, Ash would be around 12 years old right now. You don't become a master animal tamer in a couple of years, let alone monster trainer, let alone when you're a kid. Ash is admirable because he keeps trying no matter what. Japan has an ingrained cultural problem where they believe that it's better not to try at all than to try and fail, and they're trying to move away from that and teach kids otherwise. Ash exemplifies that defeat is not failure, but a learning experience. It's also admirable that he doesn't bring his old strong Pokemon into a new region, he starts from scratch so he can improve and prove his worth as a trainer.
As for replacing Ash, every protag is going to have the same generic shonen personality, so what's the fucking point?