Schweinsteiger was injured for most of the season. He's still one of the best CMs of the 5 years or so. Carrick has never been an "elite" player as much as our fans like to rave on about him. He was a decent player at best. Schweinsteiger was world class at best. And I'd be willing to bet the likes of Juventus, PSG, maybe even Bayern again would be lining up for his signature if we were to transfer list him. Carrick should have retired after the FA Cup win.
Mata, I could easily see a top Spanish club like Atletico picking him up. There was rumors about Barca aswell. Plus he's still in his 20s. Rooney? His prime is over. He's been in decline for about 4 years now.... since Ferguson retired, maybe even before that. On top of that, Rooney had his chances last season. Van Gaal did what everyone was begging for in the second half of the 14/15 season which was to sell Falcao and Van Persie and play "our best striker" Rooney up top. And look how that worked out. He couldn't score a goal from August-January. It was terrible. Yet everyone thinks he's a definite starter? This is part of the problem with United. By that logic, we should have kept Falcao. There was no difference in Falcao and the Rooney of last season. Rooney played every game and Falcao was benched after like, 3.
Mata on the other hand has never had a consistent run of games at CAM. The majority of his time at United, he's been played as a RM which is not suited for him at all. That's why Kagawa failed - these needs to be in the middle. If we play him regularly in the middle, I guarantee he will reach Chelsea figures. But it seems like nobody is good enough for United except the great Wayne Rooney. If Pogba doesn't hit the ground running, our fans will become impatient with him and those same fans will be fuming if Mourinho dares to drop Rooney after giving England vs Iceland-esque performances.
Pogba can player deeper. He's got defensive qualities so playing him as a 10 as opposed to a 8 is a waste of his overall qualities as a complete midfielder. Mata on the other hand is a natural CAM. He's by far our best option there. Look at Arsenal... they play Ramsey behind Ozil. Fairly similar comparison.