The last two able, experienced, and knowledgeable stitchers are referring to genuine industrial machines.

I'm not confused about the difference between genuine commercial / industrial machines and strong domestics. These domestics / home machines are commonly put up and labeled as "industrial" on ebay, complete with displays of multiple layers of stitched denim and belting. An ebay listing label doesn't make them industrial.

For a reality check on duty cycles, one or more of the old line mfgs, maybe Singer, gives guidance on maintenance frequency for one of their home machines:

"Once per year, or an estimated 5-8 hours of operation."

Right, that might be 1% the use of a true industrial machine, where the SM is only operated 1 shift per day, with an 40 hour work-week.