There's a big thing in France about the 1987 generation, who won the U17 Euro in 2004. This generation includes Benzema, Ben Arfa, Jeremy Menez, and Nasri among a few others. They were supposed to become world class players, and only one reached that status. Several had a lot of trouble fitting in their various teams, due to poor mentality. I think in a way, their failure will help the new generation, because as you said, Ben Arfa was supposed to go crazy high (most of the players he played with say he's one of the most gifted guy out there, Neymar even nicknamed him "o fenomeno" after a few training session in PSG) and he hardly won anything. Pretty sure youth coaches use that when they're talking to young players now.
As for Gourcuff (born in 1986, not in 1987), his career was mostly ruined by his many injuries. In Bordeaux, he was absolutely incredible, playing wonderful games against Chelsea, Juve or Bayern, world class performances after world class performances, scoring insane goals. But then he went to Lyon, where he kept on getting injured. Had also a lot of trouble getting his confidence back. I'd say Ben Arfa, Nasri or Menez had way too big egos, while Gourcuff was on the contrary too weak mentally. But yeah, in the end, they all failed to reach the goals everybody set for them when they were young, and it was in good part due to mentality issues. And as you said, I really doubt Mbappe will have the same problem. The kid's been prepared to be a superstar since he was a baby, in every aspect. There are a lot of memes in France about the way he talks during interviews, because he always sounds way too smart for a 20 year old footballer, and you can tell it's because it's already part of his training.