Gai's speed is overrated. It's the same concept with Sasori's Sound barrier emphasis. Only because Sasori's needles broke the sound barrier doesn't mean they are faster than Shinju Madara who hasn't shown to break the sound barrier, despite being capable of it without even using Shunshin. Same applies here, Madara was able to keep track of Gai's speed and was just toying around, he could've used an ST while Gai was running and made him look like a retard, but that didn't happen. Same applies here, Sasuke is likely capable of swapping places with Gai mid-Night Moth which would logically reduce his forward momentum to nothingness since he'd have to turn around. Not to mention, distorting space in NV=/= distorting it in our world, as you either need an immense mass to do so, or you need to be going at sub-relavistic speeds, or the like, neither of which Gai can do. It was simply an exaggeration. Oh, and it's a strictly linear movement which requires prep, Sasuke flicks a Shape manipulated Enton projectile and Gai's speed running into it is what causes his own downfall.
