But substack solved distribution (and community, and bookkeeping, un-distribution etc) and it solved getting paid for my writing, which is not enough to live on but its definitely significant and well appreciated. It is worth much more than its fees, because the counterfactual is that I don't have any of those things. I think it's a huge mistake to lump those together as "convenience", its a lot more than convenient!
The only important thing to me about having a non-substack website is that its good to have a place for more permanent information, lists, contact, etc. But even for many writers, that kind of stuff becomes stale so quickly that the personal sites don't tend to matter much, or even make them look worse! The floating social network spaces are much more valuable. Even losing my x.com would be much worse to my day-to-day life than losing my domain, though I may wish it were otherwise. And I cannot replicate that elsewhere. The social networks are big because they have genuine utility.