Darmian is one of the most talented right-backs available in a pretty small market for good right-backs. He's very versatile and mobile, can play left-back too. How well he adapts we don't know, but same can be said if we end up with Fabinho.
He offers the composure and leadership they have been missing in midfield more so when Carrick has been out (a lot). He's younger than Yaya Toure, who bossed the league at this age. He did look deteriorated last season so we can hope he's spent, but he is still a very good player with great technique. CM has been a weak spot for them, now with two signings + Herrera's improvement it's pretty much transformed.
No, not really. This is like "for (any potential Dutch signing), see Samaras" when there are those like Suarez and co. from the same league. Lallana, Lovren and Lambert have never shown as much as Schneiderlin who has been one of the top few holding mids in the Premier League for a while now and I think averages the most tackles. Let me put it this way - based on what we've seen, he's twice, possibly thrice the player our current holding mid Fernando is.
And Depay is also a very good talent although we won't know how good until he's played a bit in this league.
I hate United as much as anyone, but it's head in sand to say they aren't buying well. These are signings and improve on what they have. If they get a top striker and Ramos or Otamendi, this will be a worryingly good window. We just have to try and do the same. We'd be wise to sell Caballero (and buy a HG backup) and buy a high quality foreign holding mid in addition to Pogba, then we'd have a hugely competitive midfield of Pogba/Yaya/Fernandinho/high quality holding mid.