They are legit. Keep in mind that these videos are obviously done with autobhop, that doesn't take the skill away but rather makes it more competitive since the skills no longer lays in hitting perfect jumps, which is more luck than skill based, but rather you have to do good strafing, find the best routes, handle high speed, etc.
There have been players on these YouTube channels who have cheated, but they got their videos removed. the ones I linked are legit for sure.
These people have spent an insane amount of time in to Bunnyhopping, up to 10k hours.