Any 433 formation with Fred as the deepest-lying midfielder, in the environment of the PL, is simply suicidal. We would just invite any piss poor side to hit long-balls into Fred's area of responsibility where Fred will almost certainly lose the ball and then we'd have to rely on Pogba to pick up the second balls (yeah, right). Or we would have any other side that can string two passes together and beat our press have one of their forwards outmuscling Fred in between the lines and spraying passes left, right and centre to surging attackers. Chelsea and Lampard have already paid a heavy price for playing Jorginho as their deepest lying midfielder. They try to make up for it with their (at times, excellent) passing game that puts Jorginho's vision and play-making skills to very good use. Our passing game leaves a lot to be desired and just because Fred has been showing up for the ball more than any other of our midfielders, it doesn't mean that he's a good organizer from the back. At least not for a club that has any title-winning aspirations.
Then there's the question about the type of football Solskjaer wants us to play. Do we want to become a well-drilled transition side, one that will rely on stealing the ball high up the pitch and/or use aggressive off the ball movement to get the ball from our third of the pitch to the final third with as fewer touches as possible? Or do we want to establish control in the midfield and use a delicate passing game to open up tight defences? I know that it's not as black and white as it may seem and that we'll need to do both these things throughout the season. I'm talking about the team's identity, what defines us as a football side. For the most of the season, we have looked like a side that thrives on open spaces but struggles to generate them and we have also looked like a side that understands the importance of passing the ball well and with purpose but struggles to transmute theory into something tangible (whenever the level of the opponent is below average, our patterns are much more "visible" on the pitch).
Anyway, if it's the former, we can find a role for Pogba behind Bruno (assuming that Pogba wants to stay at OT). But we'll need a proper holding midfielder next to him. If it's the latter, well that will take some serious investment in the midfield. Being able to thread a pass through the eye of the needle and create something out of thin air once or twice every 90 minutes (Pogba's key passes stat) isn't the same as reading the game, predicting where the spaces/advantages are most likely to be found/created and then passing the ball and setting plays into motion. On paper, any side with Pogba in it looks like it's world-class material. In reality, his managers have to do a lot of thinking to accommodate him into their plans. When all the fine-tuning is complete, he's definitely worth it but that's what makes him such a frustrating player in the first place.
But with someone like Sancho keeping the opposition FB in check, with Martial becoming better in between the lines and with Bruno working his magic, we can potentially create the vital space Pogba needs to do his thing. From that point onward, he's got the skills and the vision to help us a lot: Long diagonals, through balls, switches of play, you name it. Fred is a difficult one because he's a very hard-working player, he wants to contribute and he loves being here but when you get down to brass tacks, he doesn't really excel at anything. Tactically, he was brought into the fray because of the injuries first Pogba and then McT (and Matic) suffered. And although he earned his place in the starting lineup, there's a reason for this.
When we have the ball, Solskjaer's system looks like this (sorry about the formatting):
------------------------Lindelof---Maguire---------------------
--------------AWB------------------------------------------------------
------------------------Fred---------Matic---------Shaw--------
--------------------------------Bruno-----------------------------------
--Greenwood------------Martial-----------Rashford-------
Bruno's importance is pretty obvious. Not only he tries to make things happen with the ball but his constant movement can trouble any defence. He will move to the right to create a numerical advantage and free up Greenwood (or AWB on the overlap) when we switch play, he will look to either set up Martial or get in the box when Tony drops deep and he has no problem moving to the left and allow Rashy to occupy the left half-space (where he's most lethal).
Now, the #10 is crucial in Solskjaer's tactics. Both Rashford and Greenwood are attackers and not the Hazard-type of wingers who will dribble their way into the box. They rely on their teammates' movement and understanding of space. In other words, Bruno has to be pretty much everywhere. It's not a bad thing but it creates a hole in the spaces between the lines that the two midfielders have to fill (when he moves either left or right which is quite often). Now, it becomes clear why Solskjaer started the season with McT and Pogba as his primary options in the midfield. McT has the physical presence and the necessary aggression to screen the defence and Pogba will get many chances to move higher up the pitch.
The thing is that McT is not a holding midfielder (yet) and the resurgence of Matic has proved just that. What does Matic bring to the table? His defensive positioning is still great and he can drop between the CBs. This last thing may seem trivial but it creates variables that have been very useful to us. Firstly, it allows AWB to be more courageous with his runs as it can secure that we'll always have three men at the back. Secondly, it creates more opportunities for both CBs to move the ball forward (which is something that Solskjaer wants and it's the main reason why he let Smalling go) and this has helped improve our first phase of build-up considerably. Neither Fred or McT can play that holding role.
This doesn't mean that Solskjaer was crazy not to trust Matic right from the get-go. Go back to where Bruno is trying to create chances in the final third. The initial plan was for Pogba to enjoy freedom in his half 8/half 10 role and play closer to the box. This can leave, the rather slow, Matic very vulnerable against counter-attacks. Either AWB or Shaw can be instructed to tuck inside and provide cover but this leaves us with fewer options in the attack. Fred is quick enough but he often gets drawn to the ball and gets bypassed. Different kind of problem, same result. Throughout the season we have seen Marcus, James and Greenwood isolated in the wide areas with the FBs hesitant to surge forward.
Where Fred has proved really valuable is in the role Pogba's injury left unoccupied. He can't match Pogba's vision and creativity but he makes up for it with his work ethic, the pressure he puts on the first attacker and his willingness to help us circulate the ball a bit better (instead of looking for killer passes all the time). And hats off to him for becoming a fan favourite. But the truth is that this specific midfield role, as Solskjaer envisions it, leaves a lot more to be desired.
I was excited about our performances just before the lockdown as everybody else but we need significant proof that this is not a period where we hit top form like the ones most teams have in their seasons. And before anyone jumps on me, this is not a dig at Solskjaer. It's a simple observation about our midfield. We hit excellent form when he first arrived here (with Pogba in Bruno's role and Herrera in Fred's plus Matic). After the wheels came off, the hope was that it hadn't been just a temporary feelgood period but we had struck gold and that a full pre-season and a transfer window would prove that. And we invested the grand amount of 0 (zero) in our midfield. Now we are where we are with 12 wins in 29 league games. Should we do the same in the next transfer window? I think we should be more clever than that.