Priority has to be starting XI. Regardless of manager, take that out of the equation for a moment.
The squad lacks individual quality and consistency across all layers of the pitch, which is kind of normal for all teams in CL positions. However United still woefully short at the forward line and central midfield. Part of it is team shape/tactics, but when just looking at the individual players, it's not good enough for United to make a step up to challenge a City/Chelsea/Liverpool next year, let alone win the league in years to come.
CB pairing is not balanced between Maguire and Lindelof. Even if Bailly sticks, there is no other recognized CB United can trust as Tuanzebe has been hit by injuries and has looked solid in only a few occasions this past season.
Need another pure central midfielder, doesn't matter if they are a DLP or CDM. A well-rounded, orthodox central midfielder who can push out a Fred or McTominay to pair with Pogba (if it's a double pivot) or just having a superior central midfielder paired with one of Fred or McTominay if Pogba is on the left of a diamond, left flank, or not at the club. Garner is too young, Matic is being phased out, Fred and McTominay are a very good option and very functional for the team, but their collective technical abilities and ability to pass throughout 90 minutes isn't good enough and limits the team going forward.
Which brings us to the forward line consisting of Rashford, Martial, Greenwood, and James. Amad is too young and totally unproven. Cannot rely on Greenwood to be consistent at a high quality yet, which is totally fine/fair, so Amad cannot have this pressure put on him either. Rashford has broken down the past two consecutive seasons and his backup is James. Martial and Greenwood can occupy the CF position, but who knows what to expect from Martial going into next season. Greenwood could take another step up, but he'll still need a viable backup whether it be Martial or someone else. So that leaves right wing/right forward a black hole. Preferably, United would need a supplier on the forward line to compliment Shaw, Bruno, and Pogba. A Saka type of player from the right would be fantastic for United. Allows for a natural service supplier on the highest level of the pitch (forward line) and one on the right side of the pitch as AWB, McTominay, and whoever the RF/RW isn't a genuine quality passer/creator (James or Greenwood - although both have improved a bit, moreso Greenwood).
Thing is, I can't trust United's recruitment team to identify and buy quality players without paying so far over the odds.