Louis van Gaal made plenty of mistakes, beginning with starting Marouane Fellaini at Anfield. At Old Trafford, he put Jesse Lingard at No. 10 and Juan Mata at right wing against James Milner at full-back. He then replaced both full-backs and a holding midfielder with like-for-like swaps when needing three goals in the second leg—a decision in keeping with his history of bizarre changes.
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However, there are also legitimate concerns about the relative lack of quality in United's current squad, so much so that it would take an act of real alchemy to bring about success without some significant upgrades.
Obviously, there are no issues in goal, assuming David De Gea remains. He may have got himself slightly out of position for Philippe Coutinho's stroke-of-half-time equaliser, but United would have been out of the tie altogether were it not for De Gea's performance in the first leg. He is a wonderful goalkeeper.
Right-back remains a problem position. Neither Antonio Valencia, Matteo Darmian nor Guillermo Varela have done enough to stake a definitive claim. Darmian and Valencia lack for attacking contribution, and Coutinho's goal emphasised Varela's rawness.
Left-back is taken care of. Between Luke Shaw and Cameron Borthwick-Jackson, there is no need for an upgrade.
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Centre-back, though, remains an area of real concern. When provided with huge amounts of cover by Van Gaal's decision to play two holding midfielders, Chris Smalling and Daley Blind looked a decent option. Smalling was United's player of the month back in October 2015, and Blind has put in a number of good showings.
But there remains lingering uncertainty. Smalling's form dipped substantially earlier this year, and Blind has been in a slump since United's visit from Watford at the beginning of March.
The latter is not a centre-back by trade. The former has shown enough quality to suggest he can cut it at the top, but he would ideally be the second-best defender in a partnership, rather than the leading man.
In central midfield, there are plenty of options, but also plenty of question marks. Bastian Schweinsteiger possesses immense quality, but he is a short-term option and clearly cannot play every game. Morgan Schneiderlin has yet to truly settle in at United. Van Gaal has often rotated him in and out of the side, thus his suitability is tough to assess.
Ander Herrera has suffered a similar fate, and his form has dipped as a result, while Michael Carrick is surely approaching the end of his top-level career. Thus, further upgrades could be needed here, unless Schneiderlin and Herrera's partnership can be developed by a new manager.
The flanks look reasonably well taken care of. There is a lot of young attacking talent coming through, although an out-and-out right-winger or right inside-forward could be a big asset to the squad. However, in Memphis Depay, Anthony Martial, Marcus Rashford, Adnan Januzaj and Andreas Pereira there are plenty of options.
This is probably an area where the squad has been made to look worse than it actually is by Van Gaal's decision-making.
Januzaj and Pereira have rarely been given a chance. The structure of the team has not been set up to support dynamic, risk-taking wing-play of the type that excites crowds. United's anaemic possession has often allowed opposition defences to set up in entrenched banks, denying the wide players space to operate.
Mata has played at right wing as a means to crowbar him into the side, which has rarely ever worked out well.
It could be the case that the quality is not of a high enough level, but it is too soon to say.
At centre-forward, Martial, Rashford and Wayne Rooney are potentially backed up by James Wilson, though his 0.4 goals per 90 Championship minutes on loan at Brighton & Hove Albion, per WhoScored.com, is decent rather than electrifying.
Martial and Rashford appear to have bright futures ahead of them, and Rooney showed he can still offer something with his burst of form in January and February. He will need to be eased out of the side, though, as the two youngsters compete to make the position their own.
Overall, the picture is clouded by Van Gaal. His style of play, his selection, his substitutions, all of these have served to inhibit the squad, to limit its best players. He has brought through plenty of youngsters but rarely built a team that serves their development.
He has taken the most creative players in and out of the side, often quick to remove them when it is not going well. But it is also clear there are a number of issues with the squad, particularly in defence—and it was in part that weakness that allowed Liverpool to brush United aside over two legs.
It will be fascinating to see what happens when a new manager gets hold of them—hopefully sooner rather than later.