This boarding mess is just plain dumb. UA goes from one extreme to the other. They just don't get it. Should start with GA enforcing the carry-on limits and sizes, and the boarding groups. Having X number of boarding groups isn't the problem, the handling of those boarding groups is.
How about this, go back to 8 boarding groups (or whatever # works) that segregate and prioritize the elites appropriately, then CC holders, then passengers without status. After all, those are only numbers on a piece of paper.
In the boarding area, instead of two aisles, go to three aisles. One aisle is reserved for BG 1 (or whatever) to use whenever they arrive, so pretty much empty after the initial boarding period.
The other two aisles allow queueing up of the next two boarding groups. Have BG2 queue up in "this" aisle, and BG3 queue up in "that" aisle. Have one agent patrolling the queues to ensure only those with correct BG are in line and bags are not oversized pulling folks out of line if their bag needs to be checked.
Boarding starts with preboards, then GS/Military, then BG1, then BG2.
Once BG2 is empty, GA invites BG4 to line up in "this" aisles, proceeds to board BG3. Once BG3 is empty, GA invites BG5 to line up in "that" aisles, and proceeds to board BG4. Etc.
I will admit, I have no idea of Southwests boarding process as I have never flown them. And I don't really know what the problem is, in terms of why it takes so long for these planes to load passengers and ready to go. So maybe my idea is cracked.
I just have to think, it boils down to creating some flow that reflects the reality of the boarding groups and the process, and then actually enforcing that flow.
Like I said, I might be cracked.
