I do feel that there is a lot of inconsistency in Ash's character between seasons, particularly in the odd-numbered seasons: in the third, fifth, and seventh generation seasons, he feels painfully inexperienced when compared to previous seasons. I suppose a general reset was necessary to make each season a good jumping-on point for newcomers to the anime, but when viewed historically it makes his character development and growth feel wildly inconsistent. I think without this it could have made the anime a more tedious watch than it was at times, though - Pikachu would have won literally every single battle it entered had that reset not happened.
Although there is the argument that they could have found more creative ways around this inevitable powercreep: Ash's final battle against Brandon had his Charizard taken out very early on, for instance. An Ash that retained his experience from each consecutive season could have made a more interesting character as well, considering how hard he took some of the losses he had when he felt he should have won: he really threw a tantrum when Brawly beat him. Having him repeatedly humbled, struggled to develop relationships with his weaker new Pokemon, resist the urge to call upon his stronger ones to just steamroll Gym Leaders, and grow as a person, would have made him a completely different character. It's a shame they never took that route, but it would have been interesting to see.