I do not think he is replaceable but I think if you can hit you are going to get close enough that having 3-4 all pro players at other positions makes you the stronger football team by a wide margin.
As for why I think those three are better we can break it down into components of football. To skip the easy one Lamar is a better runner (even though the other 3 especially Allen are quite good).
However, I would say that in terms of pocket mobility, ie being able to get out of the pocket and convert those to yards, all 3 are slightly better for different reasons with the bulk of Mahomes and Rodgers difference being because of their deep touch.
Which brings us to the deep ball where all 3 especially Rodgers and Mahomes are better. This is a tricky one to judge because all 4 can throw it a mile, and a lot of deep balls come down to who the receiver is, but Mahomes and Rodgers can flick it 50 yards in a quick release that just puts them as the top 2 in the NFL by a comfy margin.
Accuracy: I think we can agree that Lamar is the 4th most accurate of the 4 (certainly less than Rodgers and Mahomes) and just move on though Lamar over the middle is still quite accurate.
Right now I am trying to find an aspect to his game where I would say "yes Lamar is better at throwing this type of ball then Rodgers/Mahomes/Allen". I just cannot. This is not a slight to Lamar because there are 25 other QBs for whom I could not succeed at a similar test. However, if you do not have those 3 then I would think you are better with 3-4 all pro talents across the team and having a talented rookie with extra 1sts to build a stronger core I would take that.
