Just how many Facebooks and AirBnBs are there? You can look at the biggest success stories on the internet, from Google to Salesforce, and you'll find that in the vast majority, the founders had what most people would reasonably call "domain expertise." If you want to debate or exclude the concept of "domain expertise" altogether, that's fine. The number of major internet companies founded by folks with no professional experience/accomplishment is even smaller.

In any case, I respect that you're looking at this from the perspective of a tech investor in Silicon Valley, but you're in a completely different boat than prospective startup employees like the OP.

The universe of opportunities for developers is significantly greater than the universe of investment opportunities for Silicon Valley investors. There are literally countless opportunities in literally countless markets to build companies that, if not pure "tech" companies by standard Valley definition, use technology and the web to gain advantage. A lot of these would not be viable investment opportunities for YCombinator, but they will still make those who are successful in exploiting them very financially "comfortable."

Bottom line: any developer motivated in some part by a desire to make real money is doing himself a disservice by considering that the best path to financial success is to join an early-stage Silicon Valley startup for basis points in equity.