Install steam and test which of your games will run in mint. Some might require proton, but I’m sure you’ll find that you don’t need that many reboots.
In my opinion, the full potential of linux is gained via the command line. The GUI is just an abstraction layer, and various distros have various approaches to this abstraction. Comman line familiarity is far from a necessary step, but it sure is a useful one.
Yes, it would be very weird for server addresses to have the service name as a subdomain. Like a common prefix of web servers to signify that it’s serving world wide web.
On a more serious note, this used to be fairly common for many protocols to ensure loaf balancing between different protocols - you’d have one server for www, one for ftp, and so on.
Also, from an administrative point of view, it’s more manageable when you can, for example, add an entire (sub)domain to the firewall rules.