He outkicked Kejelcha in Doha
After a fast 10 000m.
Each time he had to kick in a 3000 or a 5000m he did not win.
His kick off a slow pace will not be as fierce as Barega's or Kejelcha's, no, but when the pace is honest, he has shown that he can outkick some of the top guys in the world.
Even in the Pre 2-mile that has been referenced, while I agree that he didn't really outkick Barega because Barega died, he definitely outkicked Chelimo, who has medalled twice in the 5000 and nearly outkicked Mo Farah a couple times in the process. Kejelcha is a 3:47i runner, and Cheptegei was able to kick away from him in Doha despite leading a decent portion of the race (and Kejelcha never leading, IIRC).
He's not the fastest dude in the field, and the 3000/5000 is at the bottom of his range, so when he goes up against 3000/5000 specialists, he won't have the speed. But he's so much stronger that it isn't a foregone conclusion that he'll lose if challenged near the end of the race. Speed endurance/strength is not the same thing as pure speed.