I don't think they're at odds, per se, but having been around through the original dotcom bubble, PostgreSQL (or "Postgres95," as I'm pretty sure it was still called when I was introduced to it!) was mostly known to, well, database nerds for at least the first decade of its life. One person's "solid foundation" is another person's "technically correct but practically crawling" -- a perception that, rightly or wrongly, PostgreSQL fought against for a very long time. And I think that's what OP was trying to get at: if PostgreSQL was being developed primarily by a single VC-funded company, they just might not have had the luxury to spend years building that solid foundation.

(I'll allow that as an ex-RethinkDBer, I may have some bias here: I loved many things about the product and especially about the product, but it's hard not to suspect we should have focused on speed and, y'know, revenue earlier than we did.)