The part about U.S. development is partially true. Idaho has been developing immensely, with Boise Area 10x'ing since 1930 and averaging 30% YoY population increase the past few decades.[0] If you go there, there's immense construction with frequent road closures and cranes everywhere. So while Idaho may still be dealing with the second-order effects of California's underdevelopment, I would struggle to find anywhere that's been building as much as Idaho is.
While that could be true, it wouldn't point to the root cause. There exists a limit to how fast an area can physically develop by modern construction speeds and government permitting procedures, orthogonal to the area's willingness to develop. It's possible that 600k population Boise area is unable to build as fast as California's 700k yearly exodus would like to be accommodated.
[0]https://en.wikipedia.org/wiki/Boise_metropolitan_area#Demogr...