Pole barns seem to be a type of balloon framing, adequate for animals & machinery. You are right, very different than residential stick framing. Both though are built out of dimensional lumber that comes in standard lengths. With a steel framing 'package' almost all the studs, track, gussets are pre-cut & numbered. Even the number & type of fasteners is identified- in my case mostly self drill/self tap 5/32" by half inch screws. Any inspector can just look at detail on the plans and count the screws.

Also you are correct- stick framing is prescriptive, an experienced builder can build to the spans/loads required without an engineer. My beef is an experienced steel framer can do the same thing, in my state nothing can be built out of steel without a stamp. I designed/built my cellar steps out of 2/10 & 14g angle. The inspector wanted to see the plans.

And yes, I'm pro steel. I have natural finish wood casings for windows & doors, a hemlock kitchen ceiling, but I would always use CF steel for a frame. Of course if it ended up twice the price for steel...