So, your best bet is to take the sure loser's bet and bang with a much larger and stronger opponent? Make sense. How about this: If I can't run, I would attempt to get it to the ground where I like my chances better. If I can't get it to the ground, then I get knocked out like a fool standing up. If I can run or somehow avoid the conflict--like not starting shit in a pizza place--then I do so in the first place.
Point being, if someone is going to stab me or run up from behind and hit me with a lead pipe Dick Tracy style, they can do it whether we are standing or on the ground. And if multiple opponents enter the equation, we're going to the ground anyways. Cause guess what, people don't fight fair. They aren't going to come at you one by one and let you strike with them individually. One guy will probably be striking you, while others are grabbing you and bringing you--you guessed it--to the ground.
And actually, if I'm tangled up with a guy on the ground, I have a better chance of controlling his knife or spike or syringe or whatever then if he's loose and we're standing. I know, because I've trained realistic knife defense (Straight Blast Gym defense seminar) and the first thing you do is try to grab the guy and get control of his knife hand, because if he's loose, you are getting sliced up. And if my standing advantage is that I can run away if I see the knife, why wasn't I running away in the first place if that's possible?
Also: It is not hard for a trained BJJ to bail and pop up from teh ground. I will stand up on an UNTRAINED guy all day. I know, cause I actually do it. I train with guys ranging from 6'9 and lower, and up to 350lbs. Good luck controlling me on the ground if you don't know shit.
Also: Being on the ground offers you some creative opportunites for defense, like getting the hooks in and using a guy as a shield if somebody decides to a have a stompfest. I know guys who have done this. Cops, actually. You might also slap on a lock and threaten guy's buddies that you are going to snap something off, and it will certainly help if dude you have in a lock is begging for mercy. Multiple people have posted actually having used this tactic.
In conclusion, if you think BJJ has no place in self-defense you are an absolute fucking moron. It has a HUGE place in self-defense.