I don't think anyone doubts that outliers exist. That is obvious and true in any profession.

It's more about what a "10X" is. If someone comes up with "10X developers use black background and their x key is more worn out than the e key," I think it's not unreasonable to question that.

Also the question of whether someone who's able to spit out great code really fast but is incapable of testing, documenting, or architecting something is indeed "10X".

So the question is not "do outliers exist?" but "what qualities do outliers exhibit?"