You've got it exactly right, actually. Twitter originally billed itself as a microblogging site strictly to make link-sharing and light engagement/updates easier (IIRC, users contributed some of this stuff, like the @ and # etiquette). Substack functions surprisingly well as an RSS replacement but Peak RSS was vastly better. It's just that Peak RSS was enriched by blogging which ... just died as legacy media poached the central nodes. Twitter meant there were always new nodes and weird memes and low-friction updates.