You talk as if players are either good enough or not. That isn't the case. Potential blossoms at different times depending on how they're nurtured.
Take Baines - released, brought through at Wigan correctly, given game time, now a top player.
Jagielka, deemed not good enough, went to the lower leagues early, developed properly, now a top player.
Countless other examples of players written off as teens and eventually making it. The problem with Moyes at Everton was that there were very few exceptions to this rule, and even examples of players going away and becoming good players are few and far between. That suggests the system itself was broken under Moyes and development was subject to a glass ceiling.
Imagine you're a youth player at Everton - you make turbo progress through the ranks, you hit the reserves aged 18... then you're farmed off to League 1 ad nauseum or, at best, given a place on the bench a few times. Of course you're going to stagnate as a footballer.
Adam Forshaw is the perfect example. Rocketed up the ranks, reserves in 2008-ish, got a few first team looks when it didn't matter if he came in or not, Reserve Player of the Year when he was released the very same year. Did doing the business in the reserves translate to a chance under Moyes? No, of course not. He might have made it, he might not have done - but there's no way of knowing as he wasn't given the slightest chance. You know, like Leon Osman was? He got given games in a struggling squad and I remember it as clear as day - he came on, changed games, and people were then clamouring to see more of him. And then he got his chance consistently and, in his early to mid 20's, he was a breath of fresh air - proof of a development system in action. We've seen absolutely nothing of the sort at Everton ever since!!!
Before Moyes, if players were deemed as not good enough, they were released and perhaps came back to prove us wrong. Under Moyes, it seems like players were proactively stopped from being good enough, due to a massive mistrust of youth.
Poppycock.
Please, show me the list of players that have "proven Moyes wrong".
Players are either good or not, you mention Jags and Baines, they had a will to succeed and the actual talent to do it, players ARE either good or bad, theres no middle ground.