The venue I work in most frequently has a max cap of 2000. In such a venue we still have to endure the Marshall (or Vox or Twin or Super Reverb) set on "Romulan disrupter" that requires an FOH mix SPL of 110dBA to keep up... It's one of those dubious "artistic things" typically from one trick pony players.
Is there some in-between? I'm sure that it exists, Jay, but like Sasquatch it's almost never seen and reports are anecdotal.
Can't just blame guitars though, acoustic drums are loud by nature too, and it's not their fault for doing what they need to do to get their sound. Still, I've noticed a higher level of professionalism and ability from guys who will play behind plexiglass and not take it as an affront to their ego.
The main downside to IEM-only is that it leads to guitar modelers that sound like a buzzing bee hive with a subwoofer.
I haven't yet heard an emulation strategy that sounds nearly as good as a real amp either. The best tone I've heard from guitars has consistently been from small combo amps which are well isolated and/or offstage completely.
Then I get to work with guitarists who can create almost any tone from a Pignose practice amp, 1 pedal, and their fingers.
Yes! It's the player, not the gear. I did monitors at a mid-size outdoor venue for several acts last Summer. Kenny Wayne was one, and he's this guy. His pedal setup fits in a laptop case, he used two rental combo amps behind glass, both only at "Tribble" levels, and just two guitars. He had some of the most epic, lush, 3-D tone I've heard. It translated through both IEM's and mains beautifully.
I finished a tour six weeks ago where our guitar player had a custom that was barely larger than a pig nose. He had it in a case and it was behind glass offstage. Our drummer was behind glass, even in large venues, and it was delightful. Our IEM mix was like recording in a studio, and I've never received so many compliments for great sound.
It takes a little getting used to, but isolation/IEM is really the future.