It is rather an exaggeration to say Sequoia helped YC "get off the ground." YC was 4 years old before it took any outside money and had already invested in Dropbox and Airbnb.
Another interesting new trend I’ve seen a few times recently: second-time founders who are not raising at all! Instead they are choosing to bootstrap to Series A or, use their profitability to defer raising inevitably.
You mentioned that you would write about how SV is different than what's happening at the seed stage everywhere else. What's the tl;dr of that upcoming post?