Here's an analogous question: "Are **SSH** questions really 'professional sysadmin' related?"

CPanel is ultimately a type of "remote shell", granted it's a fairly limited (specialised, if you will) shell, but it is essentialy a shell for doing common server administration tasks for webmasters.

CPanel is a tool to install softwares and edit various config files for various softwares and what does a sysadmin do essentially? Install softwares and edit various config files for various softwares.

I think the argument that "I am a professional sysadmin and I don't use cPanel, therefore cPanel is not a professional sysadmin tool" is kinda elitist. Granted cPanel is easier to use than most other sysadmin tools and is often also used by normal users and therefore it does attract a swath of low-quality questions; but that's not a reason for discrediting the tool nor does it make questions relating to cPanel off-topic. Granted often Webmasters.SE is more appropriate for many cPanel-related questions, but that does not necessarily make it off-topic either.