Writing for Substack isn't uncool. In fact if anything, it is extremely in vogue right now. But I agree with GP that eventually it will go the way of Medium, and a new "cooler" platform will take its place.
It's the professional equivalent of people writing on blogspot or wordpress.com
A real company will have the resources to setup a blog on their own domain.
Wordpress.com recently completely revamped its pricing, pissing everyone off, then walked it back. And it's unclear what motivated it, or what's to come. This is the kind of omen that preceded Patreon's fall from obvious choice to reluctant best option of a bunch of bad or incomplete solutions. Automattic's pricing is more reasonable now, but the single $180/year plan they tried and walked back from hangs over it. It tells me they wanted to shift away from casual bloggers (like someone who doesn't want to worry about maintaining a .org install) to people who are willing and able to pay triple digits for all the features for business or personal PR purposes.
DigitalOcean also has one-click installers/images available for ghost and wordpress, but would still be at least $5/mo.
Both of these options start to go back towards the burden of having to maintain them though.
I don't know if it exists, but maybe there's room for something like a desktop version of Ghost that allows you to write posts/etc locally and then publish to a static github-pages (or s3/etc) site.
Maybe I'm in a different bubble, but most of the writers I see on Substack are individuals, not people writing on behalf of companies. If anything, companies using Medium is still more popular. Substack is also quite popular in the literary and arts circles, not just tech.