Just to add a little bit more with an actual keyboard, competition isn't the only way to gain experience. Actual experience is the only way to gain experience.
So, when we talk about fighting skills, the experience being gained in competition is in punching, kicking and otherwise executing technique in a fully non-compliant, unrehearsed encounter where there is immediate, physical and mental feedback for incompetence.
If you want to learn to play golf, you have to actually play golf. If you want to learn to fly a plane, at some point you will need to actually fly a plane. But with "self defense" there is a shocking degree of cognitive dissonance. On the one hand, everyone agrees that how one trains matters, but on the other, these same people will deride competitive arts because they are unrealistic. It's mind-blowing.
The equivalent to the swimming analogy in fighting is competition vs non-competitive arts. If you've actually punched, kicked and otherwise executed technique in fully non-compliant, unrehearsed encounters, you will be better equipped to execute those techniques in a different context than someone who has waved his arms around in a convincing manner.
I have been told by "experts" here on this forum that the other stuff... the non-fighting stuff is actually pretty easy to teach, which is why they spend so much time on the "fighting" part of self defense in their training. That fighting part is the part I believe benefits the most from competition.