As someone who was on the outside looking in on this until pretty recently, but also has spent much of the last 10 years working with a variety of different YC companies, this is pretty overblown. Moreover: there are so many YC companies at this point, the rate of increase is not an especially interesting marketing fact. For what you're saying to be true, the norm would have to be selling to your batchmates, which... I mean, batchmates are friendly with each other, but they're not like, your core market, even if you're selling pickaxes and shovels.