I’m not sure why YC is an example of something that has scaled well. There’s so many companies now in each batch with 95%+ never amounting to much success. It’s not clear how the scale is helping anyone.
The key thing about networks is Metcalfe's law: the power of a network is the square of its nodes. This is also what makes the Internet more and more valuable over time.
Those things together mean scale increases value for founders, and what we've learned is those effects are most potent early.