I encourage all BJJ students to cross train in other grappling, striking, firearms, & other weapon arts.
Learn wrestling, learn Judo, learn Sambo, learn catch wrestling, learn boxing, learn thai boxing (if you can take it), learn the Savate point of view, for damn sure learn firearms which are the core of modern martial arts, and spend at least a little time with arts like fencing, Kali, Kendo, Combat de canne, and Dog Brothers.
If you are a black belt in BJJ, and you have no exposure to other areas of martial combat, then you may not realize what you are missing.
In the movie Rocky, “Mick” has “Rocky” chase a chicken. A useful drill that does not look like boxing, but may have something useful hidden within it for boxing.
Similarly, nothing teaches distance management (which is useful for the clinch) like hand to hand weapon arts.
And firearms are a very useful self-defense area to practice…
You do not not need to be an expert in all areas. As we know from BJJ, being expert in a few areas, and having a good grasp of the basics is a common approach, that often shows good results.
But, train a little with the best teachers you can in all areas.
If you became good enough for a black belt in BJJ, then you have a fine foundation in a very useful area.
But, don’t miss an opportunity to learn from the good teachers that may come in your room to learn BJJ, who may themselves be experts in the other areas.
I remain a white belt for life, and I hope you do too.