There are a lot of great BJJ practitioners as well as other athletes out there that do not do anything crossfit related. That does not mean that Crossfit doesn't work. Nor does that mean that Crossfit won't help your jiu jitsu.
My warped perspective is that while the Brazilians are great at jiu jitsu, they have not been as pro-active in developing crosstraining programs. Don't know why that is. I'm sure it will catch on eventually. I've seen more and more BJJ guys get into the crosstraining whether Crossfit or something else. In another decade it will be standard.
Most Crossfit discussions on sports all agree that if you want to get good at doing your sport, that you should practice your sport. However, that doesn't mean you should neglect GPP.
I'm a purple belt too. I haven't gotten any better technically from doing Crossfit, but my endurance, speed, strength and agility have all improved from doing crossfit and it has helped me perform better on the mat.
I teach a jiu jitsu club at Columbia University and I have been making them warm up with crossfit type workouts. Since implementing that, the level of the students has gone up tremendously. I can't support it with any real facts or science, but after 4 years of teaching this club, this year is by far the toughest group of kids.