Thing is...Is Werner really going to want to come and sit on the bench from time to time? His stock and value is high, you'd expect him to want to be a starter whenever possible. Equally, Firmino, Salah and Manes stock is high, are any of those going to want to sit out on the bench so that Werner can come in? If we don't play all 4 of them then I think someones nose will be out of joint. I'd almost say that we just don't need Werner if Mane, Salah and Firmino all remain.
tbh, I'd rather we signed Havertz (or Grealish even, for a cheaper option) for the midfield than Werner for a front line which is fine as it is.