My problem with Ash isn't even that he keeps losing the league in and of itself (though there are a mess of problems with that in its own right), it's that they never allow the character to mature in any sense. I don't just mean the "lol eternally 10" thing, Ash never feels like a more capable or fulfilled character by the time the next season starts, because they have to make him the noob again to re-experience all the early game trappings and recreate the games again, and it's reductive to the concept of writing a character: your character should change in some way as the story progresses. Whether physically, socially, or mentally, they should be in a different place when your story progresses from one point to the next. This is one credit I give to the Battle Frontier Season: Since all the facilities were "equal" in challenge and didn't have a fixed order to follow from the games, Ash was allowed to simply bring his A-Game to all of them, and it felt less like ditching his development because he brought back old team members rather than catching new ones to then ditch next season.
Here's the glaring question: If you take away the informed abilities/accomplishments like the plaques and trophy for Orange Islands, does Ash's character reflect the idea that he's grown from a previous one? I feel the answer to that tends to be no, Ash always has to meet the new rival, have trouble with him, bring only his Pikachu, etc. You can honestly watch the regions in any order and bar the occasional reference in a one-off episode with a Character of the Day, nothing about the character's makes it an issue. There's no development to be missed going from Johto to Sinnoh to Hoenn because after the Indigo League, Ash stopped developing any further despite that being one out of 7 regions spanning close to 20 seasons now.
I know the comparison is tired, but this is why the manga does better with its stories. It introduces Gold instead of having to reset Red, so you don't feel like the last story's progression was forgotten about.
Well, I'm sorry to tell you this, but that's not going to happen.
The issue is, is that you're confusing TV and other mediums like Film, and their purpose. When crafting a classical story, it's the generic arc. You get a protagonist (or some variant on the main charterer), they get a call to action, they get stronger, and then they accomplish the goal and remove the call to action (of course, it's more complex than that, but :P). Most stories follow that cycle, whether it's a classic like the Odyssey, or something modern like Harry Potter.
Mediums like movies or books are designed to do this. You go to watch or read a movie/book, and you come away satisfied after reading a story. You don't need to come back and do it again, and there's no need for you to become invested in the charterers. The plot is self-contained. Thus, in these stories, the characters can change drastically, beacuse you were introduced to them in the same sitting in which you began viewing the medium. There's no need for you to understand what has happened prior in order to understand what is happening now, because all change has happened during the same sitting.
TV however, has a vested interest in forcing you to come back. Unless you're binge watching, you have to have multiple sittings in which to enjoy the content. Thus, if anything major changes, such as if a character started becoming hyper aggressive beacuse their friend died, it's going to turn off new and returning viewers. If you're a returning viewer, the character you've invested time and effort into becoming attached to is no longer the same charterer. That can be a major issue for people who might miss an episode or two, beacuse you've lost their interest. Similarly, new viewers are going to have a hard time understanding and becoming attached to characters if they're dynamic, beacuse you need to understand the prior context if you want to understand the story. You can't just sit down and watch and episode, and still understand pretty much everything that is going on.
This is why most TV producers design their shows mostly to be contained stories, with a handful of longer arcs. They want people to keep coming back, and for people to be able to watch an episode whenever they have time and still understand everything. If can't keep viewership up, then they get canceled, where as a film doesn't have to worry about people not watching their content for the long term. Except for minor cosmetic changes, say Ash catches Hawlucha, or Finn gets a new arm, TV writers are not going to risk major changes unless they're assured large constant viewership (like TWD or GOT).
This is why the Pokemon anime is composed of self-contained stories. Kids aren't going to give that consistent viewership, they're far more likely to watch a random episode every once in a while. Thus, Ash cannot be more dynamic than cosmetic changes. And while this TV story style is alright, the longer it runs the more stale it gets (just look at the Simpsons *shudder*). Pokemon hasn't quite gotten that bad, but it's getting there.
The best option is, as people above have suggested, is to end Ash and start up a new lineage. However, the issue being, is that doing that is going to hurt the viewer base even further. It won't be the slow decline that's ongoing, but rather a sharp drop, which is going to net TPC far less money than if they just let things drag out. So, we're never going to get a more dynamic Ash, beacuse beating a dead horse and following the go to story method is far more lucrative.