BTW, what exactly did Ash-Greninja do in the end that no one else could? Olympia predicted that Ash-Greninja would end up saving the Kalos region but it didn't really do anything that notable from what I can tell. Okay, it used its power to help Ash and his other Pokemon escape but honestly it looked like at any point Alain was ready to do a heel-face turn. Then all other times it was with Alain's Mega Charizard X and Steven's Mega Metagross so it wasn't by itself doing anything nor anything that another powerful Pokemon could have done. And finally I would say the person who saved Kalos wasn't Ash-Greninja but rather Bonnie. Her bond with Squishy allowed it to free itself of the mind control and this allowed the two Zygarde Cores to create Complete Zygarde who defeated Monolith Zygarde & Lysandre and save Kalos.
What Ash-Greninja did was hogging all the screentime so a very low amount of effort was put into fight scenes not involving it by the time it became a thing.