This isn't even a technical accomplishment in any way, it's just slapping together a few managed services together to sign up someone for a newsletter. I cannot imagine being the one to maintain a signup flow like this, it certainly looks unnecessarily painful from here.
A big motivator for this was definitely just to try out Cloudflare workers and see how they are. I've set up countless servers for APIs. In terms of time, I'd say Cloudflare workers is a bit faster when you get over the initial learning curve. Obviously you could write a deploy script for a server and have it set up everything automatically, and I have done that in the past, but sometimes it's fun to try new things right?
I never intended for this to come across as a technological accomplishment. I even end the article with "That’s pretty much it. It’s fairly simple with no real catches". I'm merely presenting what I thought would be useful information for some people. Personally I think maintaining a server is more work than maintaining this, but to each their own.
In that context, setting up a VPS would now mean that you have to be responsible for a new pet, including security updates and monitoring. You would also have to change your deployment tooling / workflow to something quite different (pushing and restarting a running service, rather than just running aws s3 sync ...)
Of course I don't think I would take this approach if I already had a backend service hosting a site, but I certainly would experiment with it if I were in your situation.