TBH, haven't tested it with 4 players. With 2 players it is absolutely unplayable, no matter where you and your friend look. Even in empty version of the map in Forge with just the two of you.
But i haven't seen maps performing better with 4 players compared to 2 so i doubt it is any better.
It is pretty clear 343i didn't bother testing the game in splitscreen, the game is plagued by frame rate issues in splitscreen mode, with many stock maps being unplayable IMO (Complex, not counting how shitty it is anyway is the worst).
Oh God, this.