I have been critical of both Fred and McTominay but to be fair, we haven't been playing to their strengths.
Ole wanted to use them in a double-pivot, whereby their role would be/should be taking the ball from the CBs and progressing the ball. Now, this was never going to be a strong point for either, both look uncomfortable receiving the ball with their back to the opposition goal and McT in particular is too large to be really mobile/nimble enough to play effectively on the half-turn.
What it looks like we might do under Rangnick is look to bypass the slow build up through the midfield and instead turn oppenents round and utilise McT and Fred much higher up the pitch to go and join the press.
I would anticipate we will almost end up defending with a 4-2-4. The CF, the two wide players and one of the midfielders (Bruno, Fred, McT) will press the opposition back four/DMs and the two midfielders will be nice and high and aggressive in setting traps in the passing channels