Here's my issue: I don't disagree that competition helps. However, every time I state that, someone takes the opportunity to state that competition is better than SD training. There's zero reliable proof in either direction. All we can do is interpolate. In my experience, if someone is well-trained for self-defense, then defending against an untrained attacker is easy, except when it isn't. I've heard the same from folks who trained for competition.
Let's be clear, all competition is not equal. I won't for a moment accept that training in kicks-only competition is anything close to as useful for self-defense as either boxing, MMA, Judo, or self-defense training. Nothing wrong with it, but it's not going to prepare someone for street defense nearly as well. Still, it's better than no training, and I've seen videos of those folks using it on the street.
It's about HOW people train, and I can train with resistance without competing, and have done so. That's part of self-defense training. If it's not, then it's not really self-defense training.