I've spent most of my career bootstrapping and I don't think this is true. If you are going to be the kind of startup that raises outside funding, you're better off following the YC playbook than you are trying to build negotiating leverage by achieving PMF with a slow go-to-market. Three big things I think you're missing here: first, the relatively low cost of previous-to-priced-round funding, second, the outsized impact of social proof (from YC itself to seed funders, from YC to A-round investors, and from seed funders), and third, the marginal value of a going-concern bootstrapped business to an A-round investor, versus the ability to plausibly tell a story about rapidly growing to a point where you can earn the investor a high-multiple return on their investment.

I think it might help to remember the investment strategy VC firms have. No matter how you structure a startup, it is more likely than not to fail; that's what companies do. The winners in an investment portfolio have to pay for the losers, which mean the winners have to pay big. And funds themselves have lifespans; for several reasons, they need to reach an answer on investments within a set timespan.

I think not raising money at all is a great strategy, and when it's viable, it's probably always superior. But if you're going to raise at all, slogging it out on pure sweat equity isn't a great way to build up credibility for an A-round. It might have been in 1999, but I don't think it is now; now, I think if you want to raise an A-round, the happy path is to raise a syndicated seed round first, and clearing the way for that seed round is probably one of the 3 biggest things you get out of YC.