We've certainly mismanaged players, failed to get the best out of most of them, etc.
But I think Wan-Bissaka is also in that group of players who looks good at 'smaller' teams, when people focus more on his positives; but isn't quite good enough for the 'top' clubs, where his weaknesses are more exposed and highlighted.
He's got good physical attributes and can get up and down well - especially when he has space to run into, as he does more at the likes of Palace. And that's enough to receive praise in the media and certain level clubs. But his technical attributes are limited, and his attacking end product virtually non existent. Which, at a club like United, and compared to what the FB"s at rival clubs produce, is poor and gets criticised more than if he was at the likes of Palace.
Defensively, he's good one on ones. And again, at the likes of Palace, that's what was focused on more. At a club like United, the frequency he gets caught out of position dealing with balls from the other side gets more attention as every goal the top teams concede is a bigger thing, and more scrutinised, than the likes of Palace conceding them. So defenders weak areas there can go under the radar a bit more.
It's similar with Maguire at Leicester. We were looking to buy English, and the positive attributes of those two were being regularly highlighted. But the limitations in their games meant they were never £50m / £80m rated players. And, with those price tags, and playing at a huge clubs, comes more scrutiny on the negatives of their game and less on the positives which are good enough for a certain level - just not necessarily Man United, £50m / £80m level.
Unfortunately, with his increase in wages, there's no way a more suitable level club could afford to buy him permanently at the moment. So a loan to that mid-level PL, with us paying much of his wages, is more likely if he does leave.