The class B pic shown in your link would be a perfect candidate to retrofit to housing if it’s unrented.
According to the architectural studies I've read when I looked into this question for myself, you would be incorrect. Open floor plans are apparently pretty horrible for residential conversions. Many residential building codes require each bedroom to have a window with a screen for ventilation. Now look at that picture of the Class B. The only exposed areas that could have a window with a screen would be on the perimeter. Further, codes many have rules that say that you cannot have one bedroom accessible by passing through another, so that would exclude long skinny apartments unless the are a 1 BR. That would leave lots of square footage trapped in the middle unusable for bedrooms. Could you put windowless living rooms and kitchens there? Sure, but even then its very few residences when they could knock that building down and get many more windowed rooms on the same piece of land.
Class C's don't have these issues as they were built with small individual offices in mind and not open floorplans, which make for affordable cost effective conversion to residences.
The classifications you’re showing are classes of rentals, not building construction.
I'm no building expert, but I am not aware of a difference in "class of rental" vs "building construction" you're making the distinction of. The studies I read only referred to them by class letter and never mentioned any distinction that you're referring to.