I don't think that you're the only person left who likes Pokemon exactly the way it is. I feel the same way about the series. I love it for what it is. I don't think that I ever thought that we would see Ash becoming a Pokemon Master when it first started. I thought that it would be over after the Indigo League for some reason, but I was clearly wrong. I doubt that Ash will be leaving anything soon. I think that it helps that they change the cast with every new saga and that he gets a new Pokemon team as well. I wouldn't be surprised if Ash didn't stop exploring even if he did become a Pokemon Master. He obviously loves to explore different regions and challenge himself with new leagues. Besides, from the champions we have seen in the series, including people who have won the Grand Festivals, they still travel around, trying to grow even more as trainers.
That's a good point. Even if they replaced Ash, he would have the same kind of attitude and most likely would have his own Pikachu. It would feel just about the same in the long run. Considering that they've kept him for over ten years, I seriously doubt that they'll get rid of Ash myself.
I agree with you about Sinnoh and Kanto. Sinnoh and Hoenn have brought out some of the best episodes of the series for me. One aspect of wasted potential during Kanto for me was how they rushed the first six gym battles in thirty episodes, most of which were cheap/pity wins as well. It would have been nice to see a better way to see Ash grow from a rookie to a slightly more experienced trainer by actually winning more than three or four badges in an actual battle. It also would have been really cool if they had done something with Sliph Co, but maybe they didn't want to focus too much of Team Rocket outside of the usual trio.
While I don't remember that much of Johto outside of the later part of the saga, I agree that they could have done a much better job of the pacing, especially during Johto League Champions.
I personally think that Chaotic has some wasted potential. While the past two seasons have been much better for the series, it feels like they could focus a bit more on the creatures' lives in Perium and less on the kids battling the card game. Of course, the main purpose of the show is to promote the card game, but I think that they could still do that with the kids and monsters having more active roles more often. It also would be nice to see the world of Perium explored/explained a bit more too.