Ok, I dont get your point of view. As I dont see the need to sub path things.
What I do see is a lot of people who seem to think that a sub-path is good security, cheaper to run and lots of other things.
First off, you can get free lets encrypt certs and even a wildcard cert if you know how. Also you can get a SAN cert with a little config of certbot.
Second, you dont need an A record for every domain. You can use a c-name or even a wildcard to catch any domain name.
Then the security is all crap, if the sub path is on the internet it will get found in time. A domain is just more obvious, you can also name the sub domain anything you want. Case in point is my nextcloud on an owncloud sub domain.
If you start to look into ways to automate all that, then things are trivial to add to. I use OVH for my domains, as they provide an API that I can use with certbot to get any certificate I want for my domain. I can also use the API to provision a new subdomain, be that an A record or c-name. But I have a wildcard subdomain so that I can spin up anything on any subdomain and I dont have to do any setup.