Sorry your logic is misleading. Matic always starts but he can't play 50 games a season, which is what we typically have. Let's say he starts 35 games a season. For 30 games a season we would typically play 4231, so Pogba/Fred/Herrera/Verratti need to fight for that 2nd spot, which is precisely what we need. On the other 20 games we would typically play 433, which I assume they are big games, hence Matic always start, so should Pogba. Fred/Herrera/Verratti need to fight for the 3rd spot. Using my ratio of formation, there are 30X2 + 20X3 = 120 starting appearance for MF. Assuming Matic pocket 35, and there are 85 divided between Pogba, Fred, Herrera and Verratti. If Pogba puts his act together he might also get 35, then Herrera probably get the short straw.
Personally I have no regret on Herrera or Pogba, both have been given plenty of chances. McTom might get a few odd games here and there but he is still young and can go on loan. Mata is the odd man out, about time he moves on.