I don't know if there are many BJJ schools around that focus purely on self defense. I think most teach tournament grappling. The problem I see in a lot of tournament martial arts is the weight class limitation. Techniques you practice in your own weight class sometimes don't work on larger stronger opponents.
A common misunderstanding. In BJJ you train stuff that is designed to help you deal specifically with larger and stronger people. I regularly get huge guys come into my club and when it comes to sparring they clearly want to test the art out. Generally I have no problem subbing them out.
where the confusion comes in is the fact there are weight divisions at comps. But comps are not general training. And the reason they divide by weight is that they also divide by skill level. In other words, when skill level is approxiamtely even, of course size makes a difference.