Well as a black belt in BJJ and having spent time in the Corps I can tell you that the grappling Ive had to use in self defense really worked. Competed a few times as a blue belt but that's it. Having been in a few bar brawls, none that I started, I can tell you that there is barely enough room to punch. Best tactic is to stay alert, keep head covered and find an exit.I think a lot of people don't train in the middle ground between punching and grappling. This is wing chun's sweet spot though.
I also think people train in a way where they feel they have to have a lot of wind up to their punches in order to generate any power. You need to learn how to get a powerful punch without relying on muscle. Look at Bruce Lee's one inch punch. Something like that would be a very useful tool to beat a grappler, even if they already had you in a clinch.
Then again, when you are in a clinch or on the ground, your body mechanics won't be what they should because you are not in an ideal position...AKA, standing up and rooted in the ground. However, there are ways to train around that too.
I also like one of the previous comments that a takedown is easier than a KO. Some people are tough as hell and can take quite a beating.
Last but not least, we seem to be leaning toward grappling arts being better IN COMPETITION. In a bar fight, you can't grapple when some alpha male and his five friends are coming at you.