You say this then proceed to include seasons where Salah hardly kicked a ball at Chelsea? to make your point?
The 2 seasons were used because, as young players, you are looking at their recent progression (and to demonstrate the ability to show pedigree across multiple seasons)
And also because you only have 2 seasons of data really for Zirkzee being a starter in a top 5 league, before that he was either injured or playing in Belgium.
In any type of statistical analysis, you will find minutes to goals Salah and Jesus outdid Zrikzee in the 2 seasons before they moved clubs.
Here it is for you
Zirkzee 3693 minutes - 13 goals - 284 minutes per goal
Salah 5226 minutes - 29 goals - 180 minutes per goal (Like I said before Salah shows good goal-scoring pedigree before getting that move to Liverpool this is a goal every 2 games, he also had good assists too)
Jesus 3937 minutes (in a tougher league and as a sub) - 17 goals - 231 minutes per goal