Substack is winning because of business model innovation, and also because of market timing. Their technology isn't really an advantage compared to legacy CMS platforms - how they are employing that technology is the difference.

Medium went for a bottom-up approach, trying to monetize the content of the crowd. Substack is going for a top-down approach, grabbing writers with an existing large following and paying them top rates, which are justified by the conversion rates for their well-known creators.

Normal people might not have heard of these companies, but niche audiences certainly follow some of the specific authors/columnists/influencers and are following them onto substack with paid subscriptions.

Is that a moat, or will they jump to the next platform? A few have been poached by the NYT and other venues, so maybe the moat isn't that big.