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This. This right here. Especially with Alain never getting blamed or reprimanded for anything, even though he majorly contributed to the rise of Team Flare BY CAPTURING THE SAME ZYGARDE that Team Flare later uses! (And of course after the final battle, Z2 never brings up "oh hey, your that guy who gave me to Team Flare") Of course no one is gonna bring that up, as Alain and his Charizard are basically worshipped as gods on this forum, so whatever.
I'd argue that despite Alain's flaws, nothing negative ever truly resulted from them. He still saved Chespie, got the girl, won the League and wasn't really blamed for anyone about anything. He had flaws, but unlike Ash's they were never dealt with or acknowledged by the other characters in-universe. (Now that I think on it, this may be an unpopular opinion in and of itself...maybe).
Well, Alain worked hard to gain the ME energy to save Chespie and make Manon smile (even if it led him down the wrong path). He redeemed himself by saving Kalos, alongside Ash and co. At the end, he asked for forgiveness from Manon, and acknowledged Ash to be the superior individual in every way that counted. He gave up his Mega/Key stones. It's not perfect, but it's at least something, for a kids show, that indicates he is starting over to live in a better way (like Ash).
Im still not sure why you think Ash winning the League would've made him a sue though
I didn't say just that. Winning the league on top of his presentation throughout XY would have made him a Stu. Not winning the league (and that Wulfric first battle + fallout) is what held him back from being one.
His flaws were never recognised by the others and he was forgiven too easily for those. Powered through countless opponents with his God like Mega Charizard-X, Ash never beat him despite battling him multiple times. He was an OP Gary Stu in my opinion.
See above.
Ash obviously deserved to win more than Alain anyway. He never beat Alain before, and deserved to beat him once. There was a lot of build-up in the Ash-Greninja arc, it seemed like that would lead to achieving something very great. His maturity and competence in this series was at its peak, so he deserved to win it this time.
He was just as mature and competent in DP. The A-G arc buildup was never meant for the frog to be the most powerful, but rather for the frog to be the savior of Kalos.