It is true that most of the problems lay with mistakes made to keep Ash continually in the position of a travelling trainer with a childlike wonder, the problem is continually doing so long enough, regressing him each time will eventually lead to a point where all fans, new and old, want the character replaced. This is due to certain writing tropes called "Aesop Amnesia", "The Chris Carter Effect", and "Yo-Yo Plot Points", granted I hate the names it’s the only way to make certain people understand what I am talking about; these scenarios will eventually cause all to tire of the continuous reset of the character and diminish the viewership of the series. The fact that it has lasted this long without people growing tired of it yet is nothing short of amazing. I think many Pokémon fans are beginning to suffer from Ending Fatigue... we want to see Ash's story end, just to see his story end and for no other reason.It was the writers mistake for bringing Brock back not Ash's for trying to help May out in the beginning. Besides, I'm sure if he didn't show up he would have probably continue doing so along with Max. As far as his regression goes, this happened in every saga and will probably happen again either with him in XY or another protagonist. If the writers wanted him to succeed than he would have already. Changing main characters won't solve this problem that they seem to have.They did it poorly in Hoenn, Ash acted as the mentor all of three episodes until Brock returned. After witch he returned to business as usual. He still gave her advice, but as time went on he regressed more and more into his old patterns until around the battle with Brawly he didn't really act like a mentor at all. So no... that doesn't count.They already did that with May, does that not count? Or did you not see the Hoenn saga?I think rather than immediately replacing him, they should move Ash to the Brock role and focus on a rookie trainer. It would enable them to keep Ash, have him grow as a character and still focus on new characters.
The basic reasoning behind them not removing Ash previously is the fact that there are new viewers all the time... unfortunately they also feel to realize that with the accessibility of the internet to younger and younger fans and the growing amount of youths that base their primary opinion on what they hear and see online, added together with the numerous people online calling for the replacement of Ash will cause even the younger fans to turn against the once loved protagonist. We are headed for a perfect storm against Ash and the writers will realize it eventually, I just hope it's before it leads to the end of Pokémon.
Once again I hate using tropes when referring to things... I just don't think people have the patience to read the five page editorial I wrote on Pokémon and the current state of its primary character.