San Diego/LA strikes me as similar to Chicago/Milwaukee, DC/Baltimore, and NYC/Philadelphia as one of those markets that are essentially one metro with a legal fiction designed to keep them artificially separate
distinguish here from LA/Riverside and SF/San Jose which are even more fictional than the above
You ever hear of the Northeast Megalopolis/Northeast Corridor? The WHOLE STINKIN' REGION is just one giant metro area with a few large nodes (New York, Philadelphia, Boston, Washington, Baltimore), many smaller nodes (Providence, Hartford, Springfield, Worcester, Manchester, arguably Portland, New Haven, Bridgeport, Newark, Allentown/Bethlehem/Easton, Trenton, Reading, Wilmington, Lancaster, Harrisburg, York, Frederick, Hagerstown, Fredericksburg, arguably Richmond, and a few other peripheral cities, like Albany/Schenectady/Troy, Scranton/Wilkes-Barre, and maybe Binghamton, that might also warrant inclusion), and countless suburbs and other towns that is just one big region that has a lot of common ties within itself, especially in its two halves (with New York being the uniting city of those two halves).
The corridors you mentioned above are true megaregions or multiple center metro regions that really do have a somewhat different dynamic, due to the close ties between the metro areas, than regions that are a little further apart and/or aren't as big. (A couple others you forgot to mention are San Francisco Bay Area/Sacramento and San Antonio/Austin. The Golden Horseshoe including Toronto, Hamilton, Kitchener, St. Catherines, and arguably Buffalo is another, mostly Canadian megaregion.) And really, greater Los Angeles (which includes Orange County and the Inland Empire)/San Diego is actually Los Angeles/San Diego/Tijuana.