Put your reverse proxy in a DMZ, so that only it is directly facing the intergoogles

So what? I can still access your application through the rproxy. You're not protecting the application by doing that.

Install a single wildcard cert and easily cover any subdomains you set up

This is a way to do it but not a necessary way to do it. The rproxy has not improved security here. It's just convenient to have a single SSL endpoint.

There’s even nginx configuration files out there that will block URL’s based on regex pattern matches for suspicious strings. All of this (probably a lot more I’m missing) adds some level of layered security.

If you do that, sure. But that's not the advice given in this forum is it? It's "install an rproxy!" as though that alone has done anything useful.

For the most part people in this form seem to think that "direct access to my server" is unsafe but if you simply put a second hop in the chain that now you can sleep easily at night. And bonus points if that rproxy is a VPS or in a separate subnet!

The web browser doesn't care if the application is behind one, two or three rproxies. If I can still get to your application and guess your password or exploit a known vulnerability in your application then it's game over.