I phrased it wrong. Southampton are a really good side and should not be disparaged as just a midtable side since that is what we sort of are right now. We should not act like this is Shaw's first time playing Football now and completely discount what he did at Southampton. I also get annoyed with people that make it seem like Pogba is under pressure for the first time when he spent four seasons at the pressure cooker of Juve.
Pogba didn't meet expectation and being outright world class, but he is very good, and already at required level claiming a first indisputable first team place in our midfield. Pogba at Juventus was not an established player, but also a great player.
Schneiderlin did struggle with us while even more established at Southampton than Shaw. Shaw did well and that forced us to pay that price for him. He was unlucky with injuries, but only got few good games for us, and hadwas potentially adapted to LVG's philosophy before leg break. Changing from LVG to Mourinho style is difficult too. Even Smalling struggled when he has physical attributes fit this style to the T. Blind is not Mourinho's CB and only an attacking LB option losing his starting status under Mourinho too (where Darmian is preferred as defensive option). Change can affect any players, not just Shaw. So comparison, relating between Pogba & Shaw ain't fair for either.
The jump from Southampton to United, even when we're at low point is still difficult, is hugh. We ain't satisfied with our current position & needed sharp improvement, so the players ain't afforded the time. Less now than under SAF when we don't have a starting XI to carry the underperforming players. Even Southampton as (lower) midtable team had this stability back then.