Pogba earns 4.5mil before taxes, united offers 13mil after taxes.
Alves and Higuain are miles ahead of cuadrado and morata. They are huge upgrades.
Pjanic is much more consistant then Pogba. Not nearly as complete, but similar in terms of creativity.
I do think we will have a slightly better team even if Pogba leaves, but i don't think we made this massive jump forwards that some think we did. Morata always was a force in important CL games, it's tough to imagine that Higuain can top that for example.
Keeping Pogba is the missing piece of having a team that is better than any team that isn't Barca, Real or Bayern. Without him, without a top-class midfield, that possibility vanishes. Matic or Witsel instead of Pogba won't take the midfield to the next level, while signing Pjanic, while simultaneously keeping Pogba would.