Now that does not mean that the band doesn't have on-stage monitoring needs in order to give a good performance, but this again is where collaboration carries the day IME.
This is true, but as I like to say, "Monitors are not miracles". Musicians really need to get used to getting by with hearing less than they think they need (with wedges at least). And following the same "cut before boosting" rules used for EQ'ing. But going back to what I said before, if the stage sound is balanced and reasonable, and the monitors are good quality and properly rung out, the musicians should need minimal amounts of things in monitors. Honestly, they should really just be barely hot enough to provide some definition to the musician, over the sound of everything else in the room. If you can walk from the audience to on stage and barely hear a difference (maybe each instrument gets a little louder as you go past it), that's kind of the ideal. The wedges are just so you get some of the direct sound and it tickles your ear the right way, not like it's off in the distance, with the highs rolled way off because you're behind and to the side of the PA.
I mean, I wish people would practice as much restraint with monitors as they do with say, holiday treats. But they're more likely to say no if you ask if they really need that 3rd christmas cookie than if they need 3db more of their own lead guitar that's already the loudest thing on stage besides the cymbals. The point that something is so loud in the wedge that I start taking it out of the mains because it's already too loud at the back of the room is an issue, and under the bounds of physics and with conscientious musicians, that should literally never happen. I have had a guy ask me for more of his lead vocal in the wedge, and I'm 60 feet away at the desk, with the mains off, and I can hear his monitor clear as day. Meanwhile, do you think they were willing to turn DOWN the lead guitar amp on stage? Of course not.
It's all an eco system, and everything has to work together, but it's the sound guy who has the big picture in front of him and has the technology and know how (assuming somebody competent, which, if they aren't, the band torpedo-ing the stage sound is not going to help anyway) to pull everything together.
Anyway, I know I harp on all this stuff all the time, but it's because I keep running into it all the time, even with frankly otherwise really great bands. So if I my comments resonate with some bass player across the country, and it saves some poor sound guy at some random venue some headache and heartache, then it's worth it. Or he tells the band the same thing and the bassist says "oh yeah, I saw someone say that on the intarwebs too, so he's probably right" and everyone falls in line. My JOB is to make you sound good, and I get paid decent money to do that, because I'm not half bad. I'm DEFINITELY not there because I want to hear Wagon Wheel for the 9 millionth time, or Dont Stop Believin for the 10 millionth with the guitar 10 db too loud, or a drummer who only has 2 volumes, loud and "OMG JUST STOP PLAYING ALREADY".