At least three parts to make a concert successful:
Artists/musicians.
Organizer.
Audience.
It's the organizer that provide sound and light. Often bands have their own equipment and some members of the band knows how to deal with PA. Cut costs for the organizer and also some extra money for the band. Win-Win. It's just working when it's just one band/act.
On smaller events/venue places with 3-4 bands involved, a "back line" is necessary. The organizer tells the band what kind of equipment that is going to be used; drumkit, bass amp, guitar amp, acoustic piano, keyboard amp ...... . The band inform the organizer how many vocal microphones+stands they need. Some kind of stage plot from the band is also good for organizer. Vocal microphones are often something in the SM 58 standard. Instrument microphones in the sm 57 style.
I think the soundcheck is just for bands to make sure that things are working in the way it should. You can have a very good sound on the soundcheck. But when room/venue place is packed with 200-300 persons the sound change. And if it's noisy audience ..... an out door gig/concert.
How does a band prepare before a gig? To play/rehears in a basement, woodshed is not he same as play on a stage like 6x4 meters, 8x6 meters ..... . Sometimes horn players must hold back and sometimes blow a little bit harder (louder) ..... .
It's easy to blame the sound guys bad performance. It's often the bands that are not ready. I used to arrange RockSax workshops/days, Rock & Blues ensemble, bands to rehears with a conductor ..... . Professional players/musicians that were teaching/leading the workshops/days. Not so many bands/horn players that was interested. "We don't need Rock & Roll Saxophone/Horn workshop, .... " and when I went to listen to the band on a gig/concert they would need all help they could get. When the horns sounds like "salivation army horns" (nothing wrong with the Salivation Army and their music, I support them ...) and playing a Ray Charles/JoeCocker song, somebody must tell them what to do? I don't think it's so much about the PA/sound guys.
@rhysonsax the big band you play in sounds good.
Off topic. Far out. Maybe more a teaching post ???