So you think for example both can work with McTominay? Well we know Fred can. How about DVB? You think the partnership between DVB and McTominay is better than DVB and Fred?
I consider both Fred and McTominay as ball winning / supporting midfielders. They are not DMs. They both have good defensive skills, operate pretty much in the same area of the pitch (Fred on the left, McTominay on the right). Both contribute little going forward but are effective at moving the ball quickly. That's all similarities. McTominay has better touch and is better mid / long range passer. Fred energy is amazing so it helps the entire team.
The reason why I doubt Fred - VdB can work is because they have similar weak points - easy to dominate physically and in the air, and non existent long range passing.
McTominay - Fred will be the safest option for sure (defensively sound, ok in general). Fred - Donny will more creative but weak defensively. It might be enough against many teams mind you.
In case of McTominay - van de Beek so called double pivot (we play more of two conservative box to box), Scott takes care of fighting the midfield battle, winning headers and physical presence, while Donny helps to get the ball forward. On paper they just complement each other very well.
Any midfield setup can work against
some opponents, but McTominay - van de Beek pairing is the only one that can be a base for a team that can play
any opponent. Both low block and top tier.
Obviously that all applies to 4231. In case of 433 with single pivot (only Matic for us can play that role), it's much easier to accommodate Donny. But in that scenario there is no place for either Fred nor McTominay - they don't contribute enough going forward.