Even on a much, much smaller scale and knowing family members who worked on sound in true large scale professional settings, as the band you have absolutely no idea how it sounds to the crowd.
Worst case scenario you have no monitors and you hope for the best, a step above that you have a monitor that plays what you ask for (I hate the soundcheck phase and working out what you want the sound tech to play to you), best case professional you have inner ear monitors and it is fine tuned.
All I'm saying is that the sound team did fuck up by the sound of it but the band probably had no idea there was anything wrong.