t100 is not full of cheaters, I would say 95% of it is legit (Light DC)

But from what I personally witnessed, there is 1 known speed-hacker that has been at it since season 4 I believe
They usually reach crystal rank and then stop, but they got t100 in season 5 (V. U.)

There are no rewards for us t100 players so no big deal really, but still, SE should monitor their game mode to ensure everyone has fun.

Still, those cheaters (very few) should not be an excuse for preventing anyone to reach t100.. the leaderboard is literally free on Light/Chaos