Ash is wasted on competitive Pokémon battles.
Sure, sure, he does well, and finally got a trophy out of it, but consider the amount of Legendary Pokémon he's encountered, and not to mention, times he's had to save the world from or with said legends, Ash is a natural Pokémon Ranger. He doesn't even look for trouble, but he has more experience in Pokémon ranging than most actual rangers do. And this is in part due to his empathic nature, wherw he can gain the trust of nearly any Pokémon, be it a common Rattata, a Legendary, or even a Mythical Pokémon. Doesn't matter, Ash can and well get through to them or die trying. Once he actually did die trying, but that only slowed him down for a few minutes.
Is he a good trainer? Yes. Absolutely. But he's so much better when he's not battling for a championship. Considering the amount of Legendaries he can call friend, not to mention his Pikachu that is so far beyond what a Pikachu should be able to do and it's fairly easy to see that Ash's strength is befriending and raising Pokémon, not as much fighting with them, though he certainly can. In other words, he has all the strengths a Pokémon Ranger needs.
If they ever retire Ash from the show, I hope it's because he becomes a Ranger and shows up whe the world is at stake or a Legendary needs calming down. Because he's done that so many times already.