I went threw X recently (funnily enough, I chose Delphox and Venasaur as well), and would say that Aerodactyl is a phenomenal member of the team, but Sylveon could've been replaced by Huge Power Azumaril, which can be obtained earlier and is more useful for a team. Also, why do you use Scizor, a Pokémon you must trade for, instead of Lucario, which is far more useful and is literally handed to you? :P