There are two more key differences: Substack has serious marketing effort behind it. Big scale, well thought ought, multi-channel and multi-platform. It's the proverbial tide that rises all boats - the ones that docked at the Substack harbor, that is.
The other substantive advantage is uniform and clear user (reader) interface. The value of which cannot be over-stated for ease and please of focusing on the content, for comfortable familiarity, and for fast, smooth performance. It stands in stark contrast with ad-laden, noisy and ad-hoc interface of most online publications, be it newspapers or blogs. Its structure is very clear "flat trees", giving an almost linear navigating experience - as opposed to the multiply linked graphs of typical publications. The constrained options of Substack allow it to be, and remain, great. It even passes the "works just as well without adblock" test.
At the risk of doing it disservice by the way of risky comparison, Substack is everything that Google Amp ever wanted to be - and without the warts.