The sign was there all along, in our faces. They said in the fucking first episode it appeared in that the 'Hero' Greninja 'appeared' when the Kalos region was in danger.

Ash-Greninja was never about winning the League. Ash-Greninja's true purpose is to save Kalos.

"If it uses its power solely for itself then it will never become truly strong, it can only become strong when it's protecting those he loves" that's exactly the kind of bullshit the anime would pull and you fucking know it. The parallel in today's episode between Ash and Alain sealed the deal. Alain won because he was fighting for Manon. Ash lost because he was fighting just for himself.