A couple of thoughts...
Something to think about in self defense is that the techniques have to work, even for people who aren't fit, competitive athletes, who may have been injured, and who are facing someone who is significantly larger, and significantly stronger. (We'll ignore, for the moment complications caused by ambushes.) Maybe along the lines of a lightweight fighter facing a heavyweight... A lot of techniques practiced and trained in an MMA gym work great -- against a similarly sized fighter, when used by someone who is fit and relatively uninjured. While there aren't tons of folks much stronger than me... for a woman, or even a smaller man? Yeah, lots of bigger and stronger people out there, and odds are good that someone planning violence isn't going to pick a target who might provide a "challenge." I use my wife, my sister-in-law, my niece, and my mother as a guideline when I evaluate a proposed "self defense" move. If I don't think they could reasonably pull it off -- it doesn't pass muster, without qualifications and perhaps redesigning it. That's not to say that a person in an MMA gym can't train for self defense. They just need to look at what they're doing, and make appropriate adjustments. Like I said way back at the start -- if self defense is the goal, you need to do the research and work, and figure that out.
Ambushes and the nature of a violent attack is something else to consider. Sparring, drills, even a "real" fight all has one element in common: you know when it will happen. A real violent attack? Not so much. And that goes the same way for "regular" martial arts training, too... Again -- not an insurmountable problem (no, I'm not suggesting random attacks in the gym -- just that you have to design techniques and tactics and strategies that work with that problem -- whether that jumps over the OODA Loop through conditioned responses, or that somehow lets the defender get to the good side of the action/reaction gap.
MMA has some great aspects for training for self defense. It's very openness to new approaches, to combining and mixing techniques is a tremendous asset to finding good self defense techniques. So is training with real resistance and pressure testing of the techniques. It all comes down to training for the goal in mind.