That's interesting and to be honest I would have expected better statistcs from Mctominay. Does "lost the ball" also include misplaced passes or just lost the ball in possession?
But my "liability" comment was in terms of defensive contribution.. this season, Mctominay is better than Pogba in both tackles (2.4 per 90 minute compared to 1.9 ) and interceptions (1.4 per 90 minutes to 0.5 ). Its the same with Fred, and why it might be better to play either of them rather than Pogba where we are not in control of the midfield.
It includes being dispossessed and unsuccessful touches. Misplaced passes are included in the pass success percentage and McTominay is at 80.9% while Pogba is at 85.5%. So if you add misplaced passes it gets far worse for McTominay. The amount of tackles is also function of the ability of the team to control the midfield and not be in a position to tackle, McTominay-Fred was not a dominating midfield we had a lot less possession in midfield with them and a lot more defensive work for our midfielders and they don't play the same roles Pogba was being used higher in June and when the team was still fresh, Matic was the one covering behind Pogba-Bruno and he did better than Fred and McTominay ever could.
The liability in our midfield isn't a particular player, it's the lack of depth, Matic and Pogba were playing really well for a long time under Mourinho until the serbian lost his legs because he was overused. Personally I think that our midfield should look like that, it's basically a 433 with Bruno as the attacking CM and Pogba as a support midfielder, I feel that it is how we were trying to play in late February and June:
-------Bruno
-----------------------Pogba
---------------Matic
We absolutely need an alternative to Matic, someone that can be a co-starter because without an in form Matic we lose too much, we lose his defensive abilities and the fact that he doesn't lose the ball much. As long as our DM is fresh and competent and Pogba-Fernandes stay close to each others our midfield will overrun almost every teams. We get in trouble when they aren't compact and Matic is knackered. As for McTominay is a squad player, he is defensively inferior to Fred and Matic and offensively inferior to Pogba and Bruno, the good thing is that for short spells he can slot anywhere and give average to above average performances. But it's not a good idea to play McTominay instead of Pogba if you want to control midfield, you will lose the link between the DM and the more attacking CM because McTominay loses the ball often and he is the midfielder that who on average makes the least amount of passes, personally I would have him as the fifth option in our midfield when we add the missing DM.