Publishing can help you develop a voice, though. I'm currently reading an interesting history of the 90s riot grrl movement (Sara Marcus's Girls to the Front), and from what I can tell, publishing zines was a big part of what helped them develop a community, find friends/bandmates, hone philosophies and possible lyrical ideas, etc. In fact a few of the bands existed only in concept until they got put on the spot by someone who liked their zine enough to book them to play a gig! (Then they had to finish learning to play instruments and write some songs.)

In part I think that's because some kinds of publishing, like zines and social media, are somewhat in between pure publishing and conversation; they're not just a polished finished product, but also a way to discuss ideas and meet people.

That's a misleading dichotomy. All artists develop and mature over time, even at the start. You don't need to be fully developed to nevertheless have meaningful work and artistic talent that others would appreciate. Look at xkcd, for example, imagine if randall munroe had said "maybe I should wait until I have something more meaningful to say, and until I have better drawing skills".

Sure, maybe you don't quit your day job if you're still incubating a nascent talent, but you don't have to hide it away from the public. Indeed, one of the best ways to improve artistic skills is to merely exercise them a lot, and to get your work out in front of thoughtful critics and fans. Don't force artistic development into a waterfall process, it can be iterative and agile.

I think his general premise here is that the ease and ability with which one can generate and publish content instantaneously -replete with instant feedback loops- sets up bad mental habits and subroutines that begin to inhibit the ability for John Mayer to make great content.

There is a gestational element to most great creative work that cannot be denied. I think to protest this too much this suggests an infatuation with tools and process, not the product.