You cannot claim that for certain - we've turned many players to shit who've gone to blossom elsewhere and vice-versa. Not to mention being part of a different coaching set-up, training, team-mates, etc.
I think the proof is in the pudding so to speak.
They were not great players to start with. The hype preceded them, and the transfer frenzy took over from the reality.
In the years since they were linked, every single one has become a benchwarmers, playing some 10 games a season if that.
I very much doubt we missed a trick on any of them