As opposed to Isak and Wirtz who have been scoring bucket loads since joining. Their "best performing forwards" Ekitike and Gakpo aren't doing much better either with each having just 1 G/A than Salah in more games.
G/A
Salah 5/3
Isak 2/1
Wirtz 0/5
Ekitike 8/1
Gakpo 5/4
Put it this way, this is like having a Thierry who "wasn't performing" back at the start if the 04/05 season, as well as a couple big money forwards we bought that summer who were also not performing (with two of them combined having the same G/A), and instead chosing to bench Thierry for weeks while the others keep starting?
Yeah that wouldn't go down well with me. The response from Salah wasn't right, but it clearly isn't because he isn't performing otherwise the others aren't performing any better.
Though I agree with Meatwad that past exceptional performances and titles won does not guarantee you a starting position forever, it should give you more goodwill in the bank to keep starting over others who are also not performing but have less goodwill earned from past performances for the club.