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.
That's because raising money usually ends up being a full time job.
There's a long tradition of that and honestly not really a 2018 thing imo. What it does say is that in the preceding years many people had exits and thus the raw visible numbers have gone up compared to decades past.
Ex: CEO of previous company (founded in 2007) as 3rd time founder didn't take money until the A round and was funded by his previous exits even though we were a semiconductor startup.
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?