One thing to note is Ndombele is younger than Fernandes by a couple of years.
The issue is money. Arry mentioned it some years ago, in relation to how young players have their hunger taken away with massive paychecks. I think that is very much the issue for Ndombele. If he had to fight to survive he'd be a much better player. As things stand he can always (mentally) fall back on his paycheck "it doesn't matter I'm doing fine". I still think he wants to succeed. Just a lot of the urgency and necessity is taken away. I know we pay a lot of our wages based on performance, so hopefully that mitigates something.
Back to the original point, Ndombele is about the same age Fernandes was when he joined united, he hasn't had the two extra formative years honing his talents in easier leagues, but he can come good. Didn't Fernandes bomb himself in an earlier transfer? The major concern is Ndombele's hunger. Nuno has to press his buttons, and maybe just maybe we can see him come good in a similar way to Dele. Just do the simple things well - train well, be disciplined on the pitch - and Ndombele's natural talent will shine. The sad thing is, Ndombele finds the simple things the most difficult. If he stays I won't be sad, we have the chance of seeing one of the most talented midfielders succeed. Its the hope that kills you...