MacKenzie,

I am pretty sure that Substack is already a profitable company, while Medium continues to struggle. I'll need to source that information so please don't take my word for it (if I find the right information, I may well write a piece about it), but if that's the case then I think it is because Substack's business model is better for writers who want to build an audience organically around a topic of interest, while Medium takes writers and pits them against each other for attention and a limited money pool.

Time will tell whether Medium's approach is going to work or not, but I suspect they will wind up adopting a more Substack-like model in the future--and I think their recent emphasis on relational models is actually their first attempt to do so.

C