In the long run, I don't think it will matter. Yes everything you've said is right, but if Mbappe is the trancedent talent every top team thinks he is, then the question of who should you chase first is simple: Mbappe.
It will be the equivalent of a team being able to sign Messi 10 years ago but they are busy being worried about confirming Lahm and Marcelo.
As fantastic and trancedent as Lahm was and Marcelo is, both pale in comparison to Messi. What a trancedent offensive player can give you is 10 time more than what his defensive equal can. Especially when that equal is a fullback.
Yeah, don't rate the position :)