None of the legacy carriers use a boarding system designed for efficiency, e.g. speed and comfort. It is all about doling out tiny perks to the self-important.

While there is not enough OH space on a typical mainline single aisle aircraft to accommodate all legal carry ons, not everybody has two bags. The real culprit is the failure to strictly enforce carry on sizes. Once one's bag is stowed, it's always been my experience that the expensive and cheap seats all arrive at the same time.