Yeah if you like DP Ash more as a character or thought he had the best character development (I even agree on this point specifically) then be my guest, but let’s get 1 thing straight;
XY Ash is definitively his peak as both a trainer and person!
In XY the writers had 2 choices; have Ash be consistent with his BW self or instead have Ash be consistent with his OS - DP progression. Thankfully they discarded the witnessed BW Ash for the trash he was and chose to have XY Ash continue from where DP Ash stopped. Here’s my argument for why XY Ash is the true successor to DP Ash:
XY Ash felt like he picked up right where DP Ash left off. Even early on we see him using eerly similar tactics like using Froakie’s frubbles in novel ways like how he also used Buizel’s flotation sack in an unorthodox manner, and also his RT/DM/AS climb is an extension of the “rock climbing” that Pikachu did in Ash’s Sinnoh League battle with Paul. In terms of character, DP Ash while mature still had quite the temper especially when he thought someone was being incompetent (e.g. Dawn when they battle the tag champs the first time) or when someone’s views vastly diverged from his own (e.g. Paul with respect to philosophy on raising Pokémon) whereas XY Ash was considerably more mellow and rarely let his temper get the better of him. XY Ash was also far more accepting of contrasting views than DP Ash was. Back to the Paul example; Ash at first couldn’t stand Paul’s views on Pokémon raising though by the end of DP he had come to accept that those methods were also a legitimate way of raising Pokémon and that not everyone has to go about it like him. Similarly in XYZ Ash is familiar with Alain being highly motivated by strength yet eventhough Ash himself faltered when he began prioritizing strength too highly instead of love, Ash never chastised Alain on the matter since at this point he understands that just because he isn’t compatible with certain viewpoints, it doesn’t mean that other people can’t benefit from having those views either.
DP Ash while a brilliant tactician was very prone to anxiety when the going got tough which would hinder his thinking speed and negatively affect his Pokémon. This can be seen in his battle with Conway where he showed visible panic against Trick Room, easily lost 2 of his Pokémon, never properly countered the move and only won because of Gible’s unpredictability. Contrast this with Valerie where against Trick Room he maintained his composure, quickly thought of counter strategies for both of his Pokémon and won the battle on pure merit (he was unquestionably the more skilled trainer). While he ultimately persevered in his SL battle with Paul, Paul was initially able to effectively exploit this weakness of Ash’s during the early stages of their match by countering him every time he had a major burst of ingenuity and this resulted in Ash making a critical error with regards to the timing of Torterra’s synthesis. Even in the initial Kalos gym battles this flaw remains. Against Viola we see Ash visibly distraught after his first loss since he wasn’t able to quickly think up counters to the strategies Viola used for their rematch. Even as far as Ramos we see Ash visibly anxious when his back was against the wall and he was only able to regain his composure after encouragement from Pikachu. After this point though Ash no longer has this flaw and understands that having such an attitude will both negatively affect his judgment and his Pokémon (he even gives Sawyer advice on this in XY 75).
Even DP Ash was never able to competitively battle with the E4 with Bertha only using their battle to test and develop Ash’s observation, and she destroyed him the moment she upped the difficulty after which she told him how he still had a long way to go, as well as Flint’s Infernape casually stomping Buizel and Infernape, only getting somewhat serious against Pikachu and yet Pikachu didn’t manage to make F-Ape “sell” with any of its hits. Then we have Paul who was meant to be considered as Ash’s equal yet the Sinnoh Champion gave him a curbstomp to end all curbstomps. In XY it’s the same at first with Diantha effortlessly wrecking Ash and Pikachu though then... it happened! In XYZ 25 Ash showed for the first time in over 900 episodes that he could in fact battle competitively with trainers of the highest lvl and could realistically beat the E4s and Champions someday. In the Kalos League he had his best placement yet as runner up and while he technically was also 2nd best in Sinnoh, he got owned 6-2 by Tobias whereas in Kalos he lost in a very close 6-5 after putting up a valiant fight against the only non-E4/Champion trainer in the entire series who was able to defeat the Ace of an E4 Pokémon that too the Mega variant which would be substantially stronger (with a monster like that as an Ace Alain in all likelihood would destroy both Tobias’s Darkrai and Latios, and do the same to the rest of his team unless he had some secret weapon that’s a lot stronger than those 2 were) a.k.a Ash’s Alain feat > Ash’s Tobias feat. Ash also flat-out gave his best performance in terms of skill till date against Alain and yes I’m including Ash vs Paul SL when I say. (
https://forums.serebii.net/threads/ashs-goat-performance-as-a-trainer.662645/). Finally in the last episode of DP, Ash looks in awe at the high lvl battle that Cynthia and Flint were having, and even vicariously projects himself on to Flint in order to imagine what a battle of that caliber would feel like. Well in XYZ he didn’t have to imagine anyomore; with his Ash-Greninja being in the Champion Ace/E4 Mega Ace spectrum and Alain’s Mega Charizard X being the strongest Pokémon in existence barring Champion Mega Aces and maybe Lysandre’s Mega Red Gyarados, Ash and Alain’s climactic match in the Kalos League Finals was conducted at a
decisviely higher lvl!!!
XY truly was the culmination of Ash Ketchum as both a trainer and a human being; at the end of XYZ he already had both the skill and mentality to be a top tier trainer on par with even the E4s and Champions, and all that’s left to do is train up his Pokémon a bit more
.
