It is infinitely easier to talk than act so this critique is in deference to the entrepreneurs in the arena. With that said, I think Substack should’ve done 2 things differently 

1 - Tailor the product to power users, specifically publications (file under things that don’t scale) 

2 - Embrace advertising

I like Substack a lot. I feel like their major mistake was getting a delusional valuation and being too big

I really like a couple of their features, like showing you suggested newsletters from the author you just subscribed to. Very smart