Yeah, and it's also easy to forget that Tony Hibbert and Leon Osman were once products of the academy with little experience when Moyes took over. Then there's Anichebe and Vaughan (who was handed PL footy at age 16).
Looking at what he got wrong, you're right, there wasn't a lot of players he never used that leave the impression he got it wrong. People will obviously point to Dier and Mustafi but if you look at those two, you can see it still took them a while to get to the levels they did. Mustafi went to Sampdoria and didn't make his debut for 4 months and they were in Serie B at the time. He made one appearance in Serie B, they were promoted and he then waited until November to get his second appearance on the board. Dier went back to Sporting and initially went straight in to their B team it was a couple of months plus before he made his first team debut. What other youngsters were cast aside that went on to achieve anything of note? Obviously we will never know how things would have panned out with Stones, but other than that, the only player I can think of who achieved anything close to being at this level is Jake Bidwell.