IMHE as part of multiple YC-backed founding teams, this is a new tone from YC.
In the past they have been very condescending of anything that doesn't involve trying to be a unicorn as fast as possible. There's even a video in their catalog deriding 'lifestyle' (ie - non-vc, non-unicorn, non-blitz-scaling) startups.
It makes sense given their business model, but I found it distasteful that they were advising young, impressionable entrepreneurs to take on more risk and to move away from their core competencies: greatly reducing the entrepreneurs' own chances of success in order to give YC and their associates another lottery ticket for a billion dollar payoff.