Well, I'd say there's a big difference between sitting silently in chairs at an opera or symphony and standing/moshing/yelling loudly in extremely crowded quarters at a rock concert.
I'm not even sure how you could come up with numbers on how much viral exposure is needed to infect someone, short of controlled experiments with volunteers. The odds of killing a few volunteers seems pretty damn high, especially if you are testing with more vulnerable folks to establish a differential estimate. That's not a study I'd want to be involved in on either side of the clipboard.