Sad but eh. Charizard had more feats if you followed the Mega Evolution specials. Alain isn't some Tobias 2.0, he's proven himself to be a strong trainer.
Ash also relied on Greninja too much, this was evident when he chose Goodra (hadn't battled in ages) and Noivern (still a baby and has only won against Inkay and Doublade) for his team. Greninja would have to pick up the slack (and Pikachu, but everyone knows Pikachu puts on his plot armour whenever required). Besides...if Ash was going to win it would be when the anime ended and he would use all of his Pokemon, or at least his best from each region.
I guess you can say 'Oh, but the B/W writers wrote Ash vs Alain which is why he lost' to which you would be right (seriously go check), but Ash will always lose so long as Nintendo have games to promote. Pokemon anime is not an standalone anime, it's an advertisement. If the producers need Ash to lose to keep their advertisement ship sailing, then the writers will have to make it so (they're not going to risk their jobs against the higher ups regardless of what the fans want). If Ash won the league with this team and went to Alola, it makes no sense for him to drop off everyone bar Pikachu and possibly Greninja (if Rainbow Greninja is in Gen 7) at Oaks lab for Gen 7. Which would cut into screen time for the new Pokemon. The other option of course is to have a new protagonist in the Gen 7 anime. They've tried this already, not nearly as popular as Ash. So it makes more sense for Ash to travel into the next region.
Besides, Team Flare Arc looks amazing. I'm hyped for that, especially Lysandre vs Ash and possibly a rematch of Ash vs Alain if Alain works for Team Flare in this arc.
TLDR: I was sad, I'm ok now, producers to blame for Ash losing not writers, looking forward to Team Flare Arc.