I read the links. I don't believe that brand designers are optimizing for legibility, unless there's some real study showing sans is easier to read body text with. Designers just follow trends that have nothing to do with user experiences. People switching logos to sans are the same types of people coming up with "Metamates"; just people chasing corporate dogmas.
That gwern page is mostly rambling IMHO. Yes, there is a documented association between serifs and trust, but it is weak and mostly tested in print IIRC. I think you may be throwing the baby (real and objective improvement) out with the bathwater (fads) in the design world. There is substance there. I suggest https://watchdocumentaries.com/helvetica/
Some data: https://www.gwern.net/AB-testing#fonts