Perhaps we should bring it back to the main question, shall we?
It was weird. Since the end of BW, they have acted as if the Kalos League would finally be Ash's great victory. But we know what happened.
BW142: My dream, Pokémon Master!
- Ash reflects on his dream, remembers his friends and how they are working hard to reach theirs, and reaffirms that he will be a Pokemon Master.
- His mother shows visible sadness when he says he is going to travel again.
- Ash promises his mother that he will win the league this time.
- Ash says that he needs to get stronger.
Road to Kalos - a special about Ash's previous travels. I'm not sure, but I think they never did that at the beginning of a saga before.
XY001:We've Arrived in the Kalos Region! The Beginning of Dreams and Adventures!!
- Ash tells Viola that he wants to win a league this time.
XY040: Ash talks with Serena about his dream, saying that he is still a long way from achieving with the effort he is making, and that he needs to get stronger.
XY118: Satoshi VS Champion Carnet! VS Mega Sirnight!!
- Ash nearly defeats Diantha.
XY125: The Kalos League Begins! The Mega Lizardon Showdown: X VS Y!!
Ash faces a trainer who couldn't collect all the badges and promises to win the league.
The orange shuriken.
So, what do you think? Did they change their mind?
No one can be certain what the anime producers were thinking in develop but there are factors in play long before the League was even conceived. Namely, Alain was meant to be a major part of the XY series from the very beginning. It's just that his story doesn't coincide with Ash's journey until much, much later. And his stoic, very serious persona makes him a unique foil for Ash even when the two haven't met. Then consider how Ash was depicted in the series premiere of XY. It was clearly tailor-designed in response in BW's rather negative reception regarding Ash's portrayal in that show. Gone is the inexperienced kid and reset Pikachu. From XY and onwards, Ash and Pikachu would be portrayed as a powerful duo who could only be defeated by more powerful trainers. But he's still a klutz, prone to being childish and oblivious to things outside of Pokémon Battles.
So what does that make the XY series about? I say it's a reexamination of who Ash is and why he is the main protagonist of the series. During BW (I believe around the B2W2 animated trailer), people had been clamoring for a new protagonist for Pokémon, often some darker and edgier trainer who seems to be taking cues of Red from the Pokémon games (or rather, more specifically, Red as the fandom envisioned). They think that a kid like Ash is simply too goofy/stupid to be the protagonist of the series they wanted, especially since he still hadn't won a League yet. XY's primary goal was not have Ash win the League (since what good is a League Victory if it's not earned?) but rather to rebuild Ash's reputation as a formidable trainer that can make you believe he could win. Really, I doubts anyone here actually thought Ash could win in the Unova League after his less-than-stellar start.
That's only half of the story. The other half is his final opponent for the League, Alain. I have little doubt that Alain was designed to be Ash's Ultimate League Rival but not in a traditional sense. He serves as the fandom's wish fulfillment of an older, more badass trainer with a serious demeanor (armed with a Mega Charizard X to boot). And to ensure that Alain would be the toughest opponent that Ash would face, he's shown fightning Elite Four Pokémon (eventually beating one under Lysandre's watch). Of course, to make Ash's chances of beating Alain seem believable, Ash would have to be able to push one of the Elite Four to the brink. In this case, it was the Champion Diantha herself. That's why Gardevoir was nearly beaten by Ash-Greninja. Storywise, it stands to reason that both Ash and Alain are the strongest of the lot and both side could legitimately win...
Then was only one aspect that really decided the outcome: How does one handle victory or defeat?
The thing with Alain is that he is always focused on the destination but not the journey. Why else would he not actually be there for Mairin when she needs him the most (and instead goes on for this silly journey of winning the League to make her smile again). Whereas Ash always enjoys the journey along with the destination. He lives for the journey, the friends he's made and the battles, so much that it would be against his character to not recommend a strong trainer to partake in the League if only for the chance of facing them in battle even if it means losing the championship. In fact, I would say that he learns a lot more about himself in the Winding Woods than just remembering his childhood days. He learns why being a Pokémon trainer is so much fun for him and that it's not about winning Leagues, though that is a bonus. It's why I always mark that episode to be pinnacle of Ash's character development and why he's already the champion even before the official champion could be decided.
But for Alain, he didn't learn that lesson thanks to his long streak of wins and now that I think about it, even losing a battle wouldn't break through that thick skull of his. That's how detached he is from everyone. Defeat is just an inconvenience and all it'll really do is just him work harder and be more isolated till he gets to his goal no matter what. To really lose, he has to be on the top so he can lose everything in one fell swoop. Pride before the fall. That's why it makes sense story-wise for the way that things turn out. The only thing missing is for the trophy to be smashed into pieces when Team Flare attacked.