The link includes players with vastly lower winrate and players with high winrates but for extremely low number of games.

We need sufficient quantities to claim 99% winrate, for highly ranked players even with 200 games(which is still a low number since a single loss can massively affect results) are not even close to 80% winrate. probably with enough games it will be even lower.

Maintaining 99% winrate is extremely hard as you can only lose a single game out of 100. people get tired, try new stuff, simply don't pay attention or just get caught off guard by a new thing.

As for "malicious exploitation", it does poses a risk in some environments but the question then becomes exactly the same.

Is the AI less exploitable than the average person?

If so, it doesn't matter.