I'd say its a mixture of everything.
CB pairing is an issue. No right winger is a real problem and has been for 8/9 years, we also need a proper backup for AWB. But we do have a real, real problem with our midfield.
I insist. We don't.
We have in our senior side 3 natural DMs. 2 Natural 8s and 3 Natural 10s (one is on loan) Our problem is we never get to consistently have a dm + 8 + 10 selection because of our center defence.
Matic simply isn't cut out for the fast paced nature of the Premier League, even when it's been toned down this season because everyone is knackered he still is a weak link when on the pitch.
In his current state he'd hardly ever make the pitch if we had a defence that could operate in all games behind one defensive midfielder.
It leaves us with Pogba, McTominay and Fred as our midfield selections and all of them have flaws. When Pogba is out of the team our creativity takes a massive nosedive. We desperately need reinforcing in midfield. The problem is that we need reinforcing in severals areas of the squad and more importantly, in our first team.
Fred and mcTominay are both excellent enforcers. Our issue is our center defence is not good enough to operate behind one enforcer. For the life of me I can't understand why people constantly conflate that with the quality of the players that play infront of it in the position. Even if we could get a prime Roy Keane he'd still be forced to play alongside a Fred, Mctominay or Matic to protect it. THAT is the real problem!
The challenge we face is having huge holes needing filling despite struggling to sign more than 3/4 players a window. Further to the point, we're going to struggle with money this summer too.
The only holes we have left to fill are center defence and right winger. Then at a stretch center forward.
Right back we have Dalot and Laird returning and I'd be surprised if at least I e of them doesn't finally push AWB for the role.
Midfield? Adding midfielders does not sort out a single structural issue we have. Yet we already have 3 dms, 2 8s and 2 10s. With Garner and Mejbri ( (+ Lingard if we keep him post loan) waiting in the wings to replace the aging (Matic) and the aging 10 (Mata) in the squad long term.
It's funny how people want to ignore the blatant problem at center defence and the 8 season long right flank issue to beef up an already stacked and second strongest department in our team after goal keeper. It's baffling in the extreme.