Final straw though really was testing DB. I had a $40/mo dedicated server and I spun up their recommended few-node cluster for postgres. Query response time was something like 5x faster for the dedicated server vs their similarly priced setup. I tried upgrading the the top of the line, still much slower and at that point many multiples more expensive.
It wasn't just that though, the entire app was sluggish, whereas locally or with a dedicated box it felt incredibly snappy. I'd have had to be spending something like ~2k/mo to get their top of the line nodes across every service and still would have to accept half the speed of my entire app. The edge isn't very useful if it's not powerful!
Disclosure: I work at Vercel, and I do like what Fly.io does generally. Had these opinions well before working at Vercel was even a consideration. I think a lot of serverless/edge type hosts are hiding their true cost behind cheap low powered nodes. Especially if the most powerful nodes are still less powerful than a very mid-tier dedicated box, there goes your entire app performance.