If you have a central database, what benefits are you getting from edge compute? This is a serious question. As far as I understand edge computing is good for reducing latency. If you have to communicate with a non-edge database anyway, is there any advantage from being on the edge?
Well you can cache stuff and also use read replicas. But yes, you are correct. For 'write' it doesn't help as much to say the least. But for some (most?) sites they are 99.9% read...
Databases in Cloudflare are not edge. That is, they are tied to a central location. Where workers help is async stateless tasks. There are a lot of these (authentication, email, notifications, etc.)