The turn around is massive from the start of the season. Their defensive play has seen marked improvement. They conceded in 11 of 12 games (17 goals conceded - 1.4 per game) at the start of the season. This has been the main focal point of this season: fixing the defence. It was a necessity as they were shipping goals left, right, and centre.
It wasn't miraculously fixed because he joined; they still conceded 13 goals in the next 10 games (1.3 per game), which is actually a marginal improvement. Teams are finding it far harder to get through their defence. They have been looking more and more comfortable recently in defence, though, there are still blunders. Since lockdown, the concession has dropped to 6 goals in 8 games (0.75 per game) with 4 clean sheets.
They still have issues in terms of games where they hold the majority of the possession (Sheffield Utd and Bournemouth), which is almost exactly like we were in the first half of the season. They need new midfielders as there is no one there that is really all that good at creating chances. Lamela is truly awful at creating anything; the number of chances he messes up is astronomical. NDombele seems to have severe fitness issues, which makes him almost unplayable (Not sure you can base your team around a player who seems to only be able to play 50 minutes per game). The only one with any promise seems to be Lo Celso.
They are turning into a good counter-attacking side. They break with pace and have been causing massive troubles for their oppositions. It still needs work but it is a promising step forward. Their midfield needs a massive overhaul in the summer; if they accomplish this then I think they will be a far more dangerous team next season than people will expect.
The truth is, they could have beaten us in the first half of the match after lockdown, but Lamela could not make two simple passes to put Kane and Son through on goal for a one-on-one with De Gea. The likelihood is that at least one of those would have been a goal. Getting a proper creator will have a massive impact on their game, both on the counter and in possession., particularly with Kane (who seems to be regaining form) and Son in attack.
I think they have been slightly underestimated because of that period where their results took a downturn when they lost both Son and Kane. Massively unlucky to lose both attackers at the same time, leaving them with Bergwijn (promising), Fernandes, and Moura (wildly inconsistent). They may very well have been in with a chance of top four if that did not happen, after all they are only 4 points behind Leicester even with the awful start and that period.