All the classes I took with brownie and EBL I did from concealment with their permission. I went there to shoot how I carry with what I carry. I also shot 1911s in all them which meant I got to practice twice as many reloads. 😬 I think I did 150+ reloads in the one two day class Brownie did scoop drawing the whole time?
I went there in 2015 to learn threat-focused skills. Brownie rightfully suggested that I get an OWB holster so I could focus on the skin rather than having to be constantly adjusting my carry set-up between presentations. I believe that is the only class I've ever gone through open carrying. I was still carrying strong side IWB with an undergarment between skin and gun. After a few draws for speed, the undergarment needs readjusted, which takes time and attention. Now, I no longer have the undershirt, so it's not an issue.
One of several advantages the scoop draw affords me over my gamer draw from hands up that some other schools insist on is that I don't rake my thumb down between skin and gun. After a morning of those conventional draws, my abdomen is scraped and scratched raw.
My highest round-count class with a single stack was the FASTER I class I took this summer. Over eight hundred rounds through my .45 Shield over three days. I kept up just fine, but as you said, lots of reloads.
Years ago, I took the TDI snubby revolver class at TDI. I ran eight hundred rounds through my 940 J frame over a two day class. I would load tthiry-five or forty moon clips up at a time and fill my BDU jacket pockets with spare ammo. Everyone else was alternating on and off the line to reload speed strips and loaders while I kept shooting.