I don't know if you realise (it pretty much seems you don't) but Guardiola and management, for the most part, has looked at potential and outcasts and moulded them into his footballing philosophy, not just picked great footballers.
Great footballers are everywhere, great philosophies are not. You can take an average player with a good brain and make them better under an excellent philosophy. You can't take a dumb but excellent player and mould them via the same philosophy.
You can often see how players excelled under the Guardiola system for the first team when they've left City and don't produce after, as a general rule.