I mix our gigs with a tablet. A tablet that uses 5.8.
There's some truth to that. There are more non-overlapping channels in the space, meaning that it should be easier to carve out 'your' space in the range. However, support for simultaneous devices is again one of those things that's great for wifi generally but of no use to us in this application. A wireless guitar kit might have two transmitters at the very most. I think the record for my mixer was 4, one tablet/phone per band member on IEMs.
It's not that one doesn't have to think about this stuff, it's just that it's more complicated than "four legs good, two legs bad" that is spoken in these parts a lot. FWIW I have a few strategies that have always helped. Firstly, have a backup. When I play the kind of venue that's likely to be problematic from a wifi point of view I will always take my laptop. Hotel ballrooms, that kind of place. The laptop can be plugged into the router with an ethernet cable and I can mix a show either way. Fortunately, and not coincidentally, the kinds of places that have problematic wifi environments also tend to be the higher paying gigs. Continuity is more important and the justification for lugging backup stuff is easier. In the same way I always take a cable to use if my bass wireless fails. I have used this twice. Once was in a venue where my Line 6 G55 just would not work for some reason and once was when, 2 minutes before downbeat, I could not turn my wireless on. I used a cable and at the set break realised that the power cable had been knocked loose, if not entirely out. Secondly, and perhaps most importantly, I use a nice router. My mixer rack has a Mikrotik hap ac2 that has about 5-10 times the broadcast power of a typical home router like you get for free from your ISP. If I have to enter a wifi arms race I will win. Scan with my phone, pick the least busy channel and set the router to that. Not that it matters, it's always 7 anyway. Once that has been turned on then the instrument wireless systems will work around that.