Makes you wonder why so many anipoke fans hate Leon but love Alain
I think one of the key differences is the "stage".
Even if Alan was crazy strong, it was only at League Level. Siebold completely destroyed him and Malva was taking the piss when fighting him so >d-doesn't count.
Pretty much everyone else Alan fought was just a characters of the day, except for Trevor I suppose. So in that regard there was no hard feelings about his victories since it was against literally whos. It was just cool showcases of Mega vs Mega.
And I think this is important, but Alan's Charizard X is the first prominent Charizard there's been in the anime since Ash's one. Point being is that Charizard Shilling was just at its "beginnings" for lack of a better word so people gave it a pass.
Also, edgelord design which may look goofy since he's cosplaying as Charizard X or look "cool" for exactly the same reason.
Meanwhile Leon's crazy strong but at World Level.
Pokemon is a franchise that lives and dies by leaving up things ambiguous so Leon gets dropped out of nowhere and now this random dude who looks like a walking ad is now the supposed STRONGEST Trainer of them all and he's the STRONGEST, INVINCIBLE, UNDEFEATED, UNBEATABLE CHAMPION alongside with C-C-CHARIZARD from K-K-KANTOOOOOOOO. Just because we say so. The ambiguity is over, no more headcanon, this is what it is now. All the other Champions before him? All other Trainers? They don't reach his ankles. It ruined that previous ambiguity, and I'm sure everyone here knows that one thing people abhor is having their headcanons ruined so suddenly like that.
So now this new dude out of nowhere is now the best, has a very controversial design, his ace is not even from his region as is one Pokemon that over the years has been shoved down people's throats to newfound levels of obnoxiousness, and has an entire region where everyone worships the ground he stands on and the air his ace flies through.
Of course feathers would get ruffled.
Honestly, the only real similarities Leon and Alan have is both of them having a Charizard as an Ace. Absolutely everything else about them is different.