No, I'm just talking about Mourinho's overall track record in this case. I don't think Pochettino's record in this was all that great at Spurs, TBH, but that's another debate.
No one is saying that he can't improve established players here. That we all know he can do. It's more whether Mourinho can do so with young players and it's one thing to do with someone developed and bought from elsewhere and another straight from the club's own academy. Given Levy's track record, it's unlikely he'll get to sign many big name, established and that means, he'll have to rely on Spurs' academy, which he said he's apparently happy with. Can he really help improve young players and turn them into world beaters? History suggests no but only time will tell this time.
But apart from Ibrahimovic, what happened with Lukaku, Sanchez, Pogba under Mourinho? Turned out to be success stories, didn't they?
People have seen what happened with him at Real Madrid, Chelsea and then Man United and things always went bad under him, despite some success. Would you really want to play for a manager who has had a strong a history of throwing players under the bus, moans about a lot of things, plays boring football, creates a negative atmosphere around the club in the last 5-6 years? Players certainly don't die to play for him like they used to do a decade ago.