"It used to be the case that governments funded a lot of development of breakthrough technologies. The bad news is that they have mostly stopped"
That statement is very passive. There has been a shift in the past 30-35 years in public perception as to whether or not government is an agent of good (with noted problems) or if it is unfortunately necessary but the smaller it is the better we are all off. Unfortunately, in my view, those who believe in investing in basic research are losing out to those who believe the existing market structure is always superior.
I'm highly doubtful that YC or other similar groups really have the stomach for the long term investment that is necessary to make up for that loss of government backing. If your model is that waving a couple hundred million dollars around will induce a eureka moment in somebody smart, it is bound to be a failure. Real breakthroughs typically seem like breakthroughs but actually were the result of spending decades and a lot of money searching dead ends and making incremental progress.
At best it seems like YC can pick some slightly higher hanging fruit than the current model allows, but they can't afford to reach very high.