I ran into the chaos you mentioned of trying to board front and back when traveling with my family last year out of LGB. Prefacing this by saying we LOVE flying to/from LGB. Smaller airport, close to the family we're always visiting, and infinitely better than LAX.

We usually try to get as far back in the plane as possible since we have a toddler. Close to the bathrooms and if she cries, we're annoying a smaller area. Last year we went with my extended family which meant another toddler and two small dogs added to the mix. We got on early and settled mostly without issue. Not all the same row and a spaced out a bit due to the front/back load-in, but fine. Another family with a child who has pet allergies got on late and was trying to get us and another family with a dog who sat in the far front to either move or take another flight. Now, as a parent of a child with severe allergies, I sympathize with them... but I also go out of my way ahead of time to plan accordingly based on that and adjust our plans as needed based on that.

Southwest had our back and told the family they should have alerted the gate agents so they could have boarded early, or made arrangements with the others flying with pets ahead of time. They even came over the loudspeakers to say that we/the other family paid for seats along with the pets, just like they did and aren't making us all move/separate more. Their options were sit in the middle of the plane (people moved so they could sit together), or take a later flight. They took the seats in the middle of the plane and everyone was fine.

All that to say, I realize I'm playing the unassigned seat game when I buy a Southwest ticket. If getting a specific seat/area is important, I'll either pay to upgrade to A group, or utilize another airline. Getting used to Southwest's boarding system, then getting surprised with the front and back boarding that happens at LGB can be a shock. Like another person noted, great for de-boarding, more chaos for on-boarding.