We don't have a bad squad, but there are a lot of factors that mean those making a claim for it being a bad squad aren't exactly miles from the truth. I believe that the following players all have issues that make the squad seem poor, even if they are not always poor players:
Average Players
Valencia - I've rated him for ages, but ever since his injury he's not what he used to be, the loss of form has to be permanent by now. He's not going to be the player he was.. I still think he should stay at United, but he should rarely start games.
Young - Just not good enough and should have never been at United in the first place.
Cleverley - Is not good enough. To think he was given opportunities over Pogba for example is baffling. He is not even good enough to be considered our 4th or 5th choice central midfielder, IMO. He needs to be moved on to a club more his level, though I can't say I hate the player.
Buttner - Needs to be moved on as well.
Ageing Players
Ferdinand - End of his United career
Vidic - End of his United career
Giggs - End of his United career
Evra - Could be the end of his United career, but we need an experienced head and he is the one who should have an additional year over the others.
Injury-Prone Players
Jones
Evans
Smalling
Rafael
I rate all of these highly, but they need to get over their injury woes to really be the future of our defence. We will still need to invest in a top quality centre back or two, along with promoting Keane.
Debatable Players
Welbeck - Some people say they love Danny, others think he is a donkey that can only fall over. I'm perfectly happy for him to be where he is, though, so long as Moyes plays the squad the right way. He should rarely start games.
Fellaini - Definitely needs more time and a run of games to at least try and prove himself, so can't really make a judgement yet.
Kagawa - Does he have what it takes to make it at United? I think he does, obviously. However, we need to play a different system (the one used against Palace) to include him. However, I don't think he deserves to be first choice over any of the current front four.
We have a massive mix of absolute-top-quality, completely average at best, injury prone, and ageing players who are past their best. Add to that the debatable ones who may or may not be good enough and need to be used more/correctly, it's very difficult to assess what we have even if this side won the title last season. It's very possible Fergie did bow out at the right time.
Personally, I think we need to play the following system whenever possible:
de Gea
Rafael Smalling Jones Evra
Fletcher Carrick
Mata
Rooney Januzaj
van Persie
Next defender in line is Evans if someone is out, depending on which CB we sign in the Summer (we have to sign at least one). Obviously, Evra's place will also be questionable depending on which LB we sign (we have to sign at least one).
Next midfielder in line is Fellaini, though he would probably start a lot against the more defensive sides to offer more of an attacking threat. However, we should be looking into signing that top quality CM in the Summer (finally). I would be happy going into the season with a new marque CM signing, Carrick, Fletcher, Fellaini, and Powell (with Jones also able to cover in some games).
The next attacking player to start games would be Kagawa. This is so we play the same system! He swaps with anyone in that front four, with Rooney going up front if that player is RvP. I keep saying 'start games' for a reason. We want to play this system whenever possible, but will it always work? No. Moyes' subs always seem to be like-for-like, which rarely changes much. That player will play in the same way, so the defender, while tired, will not have to change what they're doing. Would I bring Kagawa on in a game to change it? Honestly, no. I'd rather bring on Valencia to add proper width in a game that needs changing and to be stretched. This is drifting away from Plan A during the game which Moyes never seems to do. Obviously, Hernandez would be next if two of the aforementioned five cannot play for whatever reason.
Also, when we start Valencia/Young/Cleverley, we don't (or at least rarely) win. I hope the Olympiakos game finally shows Moyes this. Against the Greeks, Moyes chose to be cautious away from home, which Fergie may well have done himself. However, after a win against Palace the game before with the system we've wanted to see all season, the easier change was probably Kagawa > Mata and go at them again. Didn't happen, so we'll never know how it would have turned out.
I've not mentioned Zaha, Nani, Lingard, or Varela. I think Zaha, Nani, and Lingard could/should all stay. Young should be sold, and these guys should be given the chance to pressure Valencia for his place (or be back-up to Rafael over playing CB's there in Varela's case).
I think this is at least a pretty accurate assessment of our squad. Do I think it is a million miles off challenging for trophies again? No. But we do need to sign four or five players of as good as or better quality than what we can offer in the first-11 I posted above (in defence and midfield).