Within the context of my work, at the level of maintaining and creating the markup col-xs-4 has a much clearer meaning than main-sidebar and it is much more reusable.

It's almost irrelevant from the standpoint of interacting or consuming the markup, and even then there is no injection against telling the world an element is a main-sidebar in addition to being a col-xs-4 which will pull-left and be a list-unstyled.

Semantic HTML doesn't necessarily equate to being more maintainable/scrapable. Have you ever come across the mess trying to emulate table-like behaviour in css with spans/divs?