My impression is that most people, as in a majority, aren't using Jane Street's Base and Core. Maybe some or even many, but not most, and specially not in the FOSS ecosystem. I think this idea comes from so many learning materials using their libs, you feel kind of funneled towards them at the start.

But yes, the standard library has added many helper functions that were sorely needed during the last few years, and the upcoming 5.4 keeps adding more. Still not as many goodies as Jane Street's libraries, but nowadays I don't miss them as long as I can use just a few small libraries, mostly by dbunzli and c-cube.