I can't believe I missed this little win. My new iPad AIR's, and Pro support 6Ghz. I am thinking of picking up a 6Ghz Microtik AP. That should solve the audience degradation issue. Just the engineer will be on the 6 Ghz network. In my experience the only time it is important is setting up the monitors and they are mostly onstage. FOH work takes place at (drum roll) FOH.
6GHz WIFI would help against WIFI congestion in the 5ghz band, but range definitely requires line of sight. Through a sea of people, chances are your device will drop down to 5ghz anyway. On stage if the access point is on stage, you should be able to get 6ghz to work well.