BJJ is the BEST self defense/offense art in the world. why do you think all the UFC fighters use it?
Because it works well it in a ring, one on one, against a skilled opponent, within a set of rules when said event goes to the ground.
It is very dangerous to adapt what folks do in any sport and assume it would be "the best" for a different situation. Competitors do whatever works best for their competition because that gets them paid.
Interestingly, BJJ dominated early on in UFC because most people didn't know how to defend against it. Soon everybody was training it and it no longer dominated as a stand alone art. Now, you have to have a good standing game (boxing/muay thai) clinch game, takedowns and defenses as well as ground game where BJJ works quite well. A new term was coined to cover this by calling it 'Mixed Martial Arts". I also find it interesting that early on (and still?) the guard position was considered a position of advantage though not as good as the mount. I watched a lot of recent PRIDE and UFC fights and the guy in the guard is certainly not in an advantageous position. Many KO's and beat downs have been administered from within someone's guard.
I'm not knocking BJJ, you just have to compare apples to apples. The best form of defense for the street is something that takes into account the possibility of multiple armed opponents, short time frames and rapidly changing situations. Awareness/avoidance, positive mindset, tools (a firearm is best) and H to H skills developed for the realities of a hostile situation, as opposed to a sport.
I try to look at fighting systems and skills as objectively as possible...after all the bad guys don't care what
I think is the ultimate fighting style. I will either be breathing afterward or not.