I only have a mild understanding of that stuff. My guess is that putting the speakers in a nice equidistant pattern, isn't the best idea for a highly reflective, symmetrical, room. The sound waves are more prone to bouncing at the same time, and canceling certain frequencies. While thats bad? Bouncing at different times can cause some wonky phase issues, as well.
The biggest issue should be the long low frequency waves. Its issues here that can make things a mushy hollow mess. In a studio, the solution is bass traps in the reflective corners to absorb some of those low freq waves, and less flat surfaces. In the Dome? The answer is to pack the damn place. Start filling up those corners? Yeah. The PA should sound better. In terms of crowd noise? I'll take no sound treatment, as the origin of every voice is a different location and can be loud as holy h3ll. Fill the place up, and that human sound treatment should help make the sound system a bit more clear.