It's one of those things, where the more personal brand building you do (speaking, posting on LinkedIn to a degree, tweeting), the more of a negative signal it probably is, with a few notable exceptions (Keith Rabois for example stands out as a VC with a good track record, yet posts a fair bit).
I do sales recruiting. It's never the strongest startups, that are doing the best that have executives and VPs all posting content 24/7.
To that degree, I have a friend who is a personal trainer at Equinox, who essentially said the same thing in the health and fitness world - the people who are posting the most impressive work on social media, actually tend to have fairly lagging results in the real world.
Also, final point, it's not really 30 under 30, it's 600 under 30, and it's a bit ridiculous. You can't really compare someone like Kylie Jenner or Lil Uzi Vert or Alexandria Ocasio-Cortez with someone who runs a startup that sells socks online.