I'm not the best person to ask but I believe it helps a lot! How much signal it adds, relative to others, I couldn't say. But obviously they should mention it in their application.

The ability to make something people want is so central to what YC is looking for that it's the company motto; and sooner or later "want" has to mean "want enough to pay for". Sounds like your friends are already there.

Biases are the result of our collective experiences, exposures & limitations accumulated over time. And we all have inherent biases to some degree shaped by our past & present, hence biases with all its flaws is a mental apparatus that people employ to understand stuffs. As such YC or any VCs aren’t immune to forming biases of their own. And given the massive volume of applications they have to go through under time constraints; they must definitely take into account multiple factors and signals that aligns with their biases in the context of their past successes.. And whatever biases that’s taken shape over time, as long as they are right most of the time, it does make it reasonable albeit it’s inherent flaws which might miss out on some exceptional founders in few cases.

However biases mostly work in information vacuum or when there’s limited set of information to take way from on ideas that are really early or unexplored. I imagine measurable results on the context of your startup idea is the best antidote to YC biases in most cases. For founders lacking in other aspects; I imagine the only viable option is to weigh in with quantifiable results. YC and other VCs might have their biases in some aspects, but there’s one common bias everyone is victim to which is “RESULTS”. So for simple founders like me who is limited by the structure of the application process, I have found a loophole which is for every section that vaguely masks your background or accomplishments, there are also sections that asks for results and numbers which is where you can derive favorable outcome from. And for that very reason, I am trying to game YC biases by focusing primarily on results.