Why would you be filling out a PhD application if you already had an offer letter from Google or YCombinator?
I left grad school to work in industry, but I’m not so naive as to think that everyone shares my preferences. I have friends who turned down Google offers c. 2001 to go to grad school, and they’ve never regretted that decision. (And I don’t regret the time I spent in grad school before leaving, either).
btw i'm a big fan of jeff's approach and hope it works out well.