I'm sure there's a more thorough, less flawed way to do this but I went back and looked at the starting lineup for United last season starting with Ole's first game in charge.
Cardiff (5-1 W): Shaw, Jones, Lindelof, Young, Pogba, Matic, Herrera, Martial, Rashford, Lingard. (Lingard scored 2, Rashford, Martial, and Herrera each scored 1)
Huddersfield (3-1 W): Shaw, Jones, Lindelof, Dalot, Matic, Pogba, Fred, Martial, Rashford, Lingard (Pogba with 2 and Matic with the 3rd)
Bournemouth (4-1 W): Shaw, Lindelof, Bailly, Young, Pogba, Matic, Herrera, Martial, Rashford, Lingard (Pogba with 2, Rashford and Lukaku...who came on in the 70th...with the others)
Newcastle (2-0 W): Shaw, Jones, Lindelof, Valencia, Matic, Herrera, Pogba, Martial, Rashford, Mata (Lukaku...who came on in the 63rd....and Rashford with the goals)
Reading (2-0 W): Young, Jones, Darmian, Dalot, Fred, Perreira, McTominay, Sanchez, Lukaku, Mata (Lukaku and Mata with the goals)
Spurs (1-0 W): Shaw, Jones, Lindelof, Young, Pogba, Matic, Herrera, Lingard, Rashford, Martial (Rashford with the goal)
Brighton (2-1 W): Dalot, Jones, Lindelof, Young, Pogba, Matic, Herrera, Martial, Rashford, Lingard (Pogba PK and Rashford with the goals)
Arsenal (3-1 W): Shaw, Lindelof, Bailly, Young, Pogba, Matic, Herrera, Lingard, Sanchez, Lukaku (Sanchez, Lingard, Martial with the goals)
Burnley (2-2 D): Shaw, Jones, Lindelof, Young, Matic, Pogba, Perreira, Rashford, Lukaku, Mata (Pogba PK and Lindelof)
That takes us up to the end of January. The results continue to be pretty good until atfer the PSG turnaround in mid-March. But that's 9 games at the start of Ole's tenure and I think adding the next 6 games through the 2nd leg of PSG would show a similar pattern. Yes he has had injuries this season (for sure) and yes there are some players who played regularly in that run that aren't on the team today. But other than Herrera, I don't see a single front 6 player in those starting lineups who isn't on the roster today. You can't blame Ole for injuries to Martial and Pogba. But to say that the front 6 talent is drastically worse than it was then seems wrong because it hasn't changed all that much. Lukaku and Sanchez were part time players at best who only really started FA Cup games. Rashford, Lingard, Mata, Matic, etc. etc. etc. are all playing horribly now but they didn't all forget to play football. If you have a bunch of players whose form has fallen off a cliff, it just can't be down to the players and not at all on the manager's shoulders. We can't be saying that any other manager would also have seen the form of those players drop so drastically. While I absolutely love Ander Herrera and think he's sorely missed, we can't be saying that his absence is the primary reason why these 9 games are so completely opposite from the 8 games that started this season and we can't be saying that any other manager would've suffered a similar fate without him. I just don't see how any of that is logical.