Peaked? I am not so sure about that. You missed a crucial factor that is an essential part of the mix in The Valley.
There was a serious study done a few years ago that sought to isolate the magic factors that make The Valley what it is. The single most vital factor found were the universities located in the Bay Area.
Given that two of the top ten tech universities on the planet, Stanford and Cal, are located there makes a significant difference. Furthermore, there are several others in the region that are very well respected too. Consequently, the very brightest in the world fight to get in and if the do, migrate.
While in the Bay Area they fall in love with it and want to stay. Also, they are heavily recruited by the local companies.
That pool of talent cream is not going away.
Also, it is a well known fact that Valley VCs like to have the ability to walk into their investments on short notice. Actual face time and physical proximity are still quite important.
Consequently, your hypothesis about peaking is suspect.
Maybe it’s more like other areas are becoming more robust.