I've been using Caddy for personal projects and I don't even think about HTTPS anymore. Except when I have to use another web server at work :-/
The problem is that letsencrypt does not offer url based authentification for wildcard certs.
So you have to temper with your DNS infrastructure so that you can automate DNS updates for your domain.
For good reason though. You shouldn't be able to get a cert for a domain you cannot prove you control. Lots of people have webserver access to a specific domain but not all subdomains.
I am not aware of any service that allows that.
Can you give an example? What do you mean by "lots of people"?