Vidal joined them at 28. It's not like he has deteriorated. He still plays for a title winning team that can win CL.
As for Pogba, it's getting better and better for him. He's only 24 years old. I don't know how can people make premature judgements on someone that young. He's one of their best players afterall. If he had flopped massively like one of those Dortmund players, it would've been a different argument but he hasn't.
In the end, money prevails. Just look at City and PSG. Players would be more than happy to be on these rich teams with high ambitions. Pogba is a bit of a cunt but I am sure as hell he doesn't regret his choice.