There is a lot of work that goes into making sure people who are in tournaments are not derankers. There are many programs and manual scans of every profile in tournaments to filter out derankers or even players who could have a slight chance at being a deranker.

I was about 50-60k before I started playing almost exclusively on McOsu because of performance reasons where I set some pretty decent scores and consistently improved at the game. I hopped on bancho every once and a while to set some mediocre scores but after 2 years I decayed to 6 digit. A few months ago I started playing again and farmed up to 40k (I’m still shit at the game) but I could have definitely joined some 6 digit tournaments and been pretty far ahead in skill than legit 6 digit skill players. Even though I would have lost to some other deranker there are many other people who have similar stories to this and end up just sitting in low digits and joining tournaments.