One can put together a set of (Fast)CGI scripts in almost any language, given environment variables and some IPC is supported (IDK what IPC FastCGI uses exactly, bug CGI is envvars). Same goes with exposing a custom socket server. I guess people associate languages with frameworks and that's why they think these things are not possible in them. Or they like the <?php ?> style intermingling of 4 programming languages, which is a pathetic bad practice that turns the program into a pseudo-quine immediately. Just read the source of a WordPress plugin (keep a nylon bag handy because it's gonna give you nausea, to say the least).

As someone in a position who's primary job has [had] little to do with WordPress plugin work, but is at the same time increasingly exposed to that due to sales department directives...

you've understated it.

And while I'm not a huge fan of working in PHP, it has its place— my remark is unrelated to that.

Except OP made no mention of Wordpress, its notoriously bad and any decent developer who also happens to use PHP knows not to touch it with a ten foot pole.