Still irrelevant to a coop conversation thread, but I've seen people Solo 9-Helldive. They are beasts, but the people going for the highest difficulty usually are. Not everyone is cut out for any given games max level, that's part of how difficulty levels work, you find the place that challenges you in an achievable way. "I" for instance am not cut out for Legendary difficulty in any Halo campaign. And 9-Helldive with a full team is going to be dicy for me and I'm probably going to be getting carried a bit.