Yes people train how they fight, if you punch a boxer on the street he's more than likely to pound you with 3 or 4 combos before he even knows what he's doing because of training.
I'll not say it's totally useless, because it does take a deal of skill to learn timing and entry of a person. Plus, in certain cases, people tend to fight the way they train. If you never used elbows, knees, hits to the throat while sparring, you might not do so in a real fight. Notice I said "might" I did alot of sparring in my youth and enjoyed it, but right now, I'm a little too old to be sparring.
Grappling isn't always about lying on your back trying to armbar someone.
Grappling is a good skill set to learn, and I agree, but I don't want to get into a grappling match in the street and get stomped out by his friends. But I agree that it is a good skill set to learn. I like your train of thought and I appreciate chatting with you.