I think what people are saying is not that they think he'll beat Khabib but he brings a fight and a test for Khabib which is the kind of things we need and where Justin is at the moment because of his wrestling background he has it'll be an interesting fight with an angle where he could really challenge Khabib.
That's not to say he would beat him, Khabib could quite possibly make him look like every other opponent but Khabib tends to get his opponents down quick and once they do they become tired very fast and then easier to take down and we know how the fight is going where as if Khabib has trouble getting Gaethje down because of his wrestling background and TD defence we could see something different here.
I think that's what people mean, well from my perspective anyway this is why it should happen because Gaethje could challenge this and we could see a different Khabib.
Honestly if Gillespie was up there or Askren or Maia were in this weight class among the top then that would be amazing and if Khabib dominates them too, well fair play to him he's the best without doubt.
I'm sure you get what I mean