I think you might be right. You'd probably fail. Maybe not. Depends on how close that competition ruleset is to what you know how to do. If you have never grappled at all, and your only experience as a fighter is striking "on the street", and the competition were BJJ, you would almost certainly fail. This seems obvious, but to be clear, it's because the experience you have is not similar to the experience you need in the new context.
Let's make the analogy a little closer to what happens in "self defense." What if you were required to compete with no advance notice, and the stakes were very high for a loss. You're walking along and out of nowhere, you are pulled into an MMA school and made to compete in an MMA match. All they will tell you is if you lose your first match (by DQ or anything else), they beat you and kill your dog. You have no idea who you're fighting against, not his skill level, his size, his level of fitness... nothing. You're just thrown in, told to compete, and informed that you do not want to lose, or else.
As I said, all experience is of some value. But some is more relevant than other's, and there is a difference between academic experience and practical experience.
To answer your question, I'd say more than most, and not as much as some. I was always fighting someone until high school. By the time I got to high school, I was better equipped to manage the gangs, guns, knives, and fights. I still got into a few fights, but talked my way out of most situations. I smoked weed and skipped classes a lot, so when you hang out in pool halls and in dangerous areas, trouble was unavoidable sometimes. I've had knives and guns pulled on me, and fortunately, have been able to manage those situations in one way or another. I also got into some more constructive activities, like the wrestling team and a few years of wing chun. In the military, I found myself in fights more often than I liked, because my friends were drunk idiots. We also had issues in some big cities, because it was Germany during the cold war, and not everyone liked Americans. After that, I have a different kind of experience working for several years with people who are disabled, often homeless, often addicted to alcohol, drugs, or both, and who could be very unpredictable.
But overall, the last 20 years or so have been very quiet.
