First of all the "if he lets in one of those..." argument is nonsense.
Its as much nonsense as being adamant that a different keeper would have lead to a different outcome. You can't know what would have happened and AM still only needed that one goal. I'm sure if Salah, Mane or Firmino weren't playing you would be sitting here saying "Mane would have put those chances away" and such other speculative phrases and yet they missed a load of good chances.