Big fan of Kroos, him not pressing or struggling as a CDM or without someone to press next to him isn't exactly new information those who watched him at Bayern, or even his loan spell at Leverkusen would see that.
He's there to shift the ball stretch fullbacks and not misplace the pass, in terms of "total football" and smothering the opponent that's the kind of team Kroos belongs in, that's why he was "perfect" at Bayern.
He's the best deep lying playmaker there is, in terms of vision and carving opening teams that would lie with Messi currently but to spray passes around and stretch teams its Kroos (from a deep position).
I think interestingly enough with Kroos development if you remember the politics of him leaving Bayern it's that the board wouldn't meet his wage demands.
Bayern have "Bands" of pay in terms of your profile as a player, how long you've been there and Gotze was on more money when he was younger, and at the club a lesser amount of time, Kroos didn't like the injustice and left.
Pep did say "I want you to stay, I can make you a better player" along those lines to the press about Kroos and I think partially that's to do with his movement and pressing but ultimately I think that's just not him and you need someone along side him to do the dirty work.
Great player, perfect technique (I could watch him pass, take free-kicks and corners all day), not the quickest or the one to put tackles in but for what he offers he's great, I can see why someone like Herrera is probably a better fit at united, although if there were quick wingers that are lethal on the break Kroos would be your go to guy.
There's a gulf in class with Barcelonas midfield but you'd have to say if you had a box to box player (Herrera, Koke, Pogba, Vidal(before his move) alongside Kroos and a CDM like Scheiderlin it'd work.