It has the same volume control as pretty much anything else: your operating system’s.

Also, hard to take someone seriously when they use the word "awful" to describe the lack of some minor UI enhancement.

Well, hard to take someone seriously when they don't understand that it's not a minor UI enhancement.

Call it a major UI enhancement. Is it still appropriate use of "awful"?

In my opinion yes. There's trend on dumbing down media UI on desktop, even though it doesn't have restrictions of mobile, with instagram being prime example - no volume control and no ability to move position. It's their choice for UI not technical problem. I have several sound sources - couple of sites in tabs that don't have volume control, media player, notification sounds, etc. They are all set in balance to my liking and I don't want to fiddle with global volume for every site.

And that's very inconvenient.

I don't get that (maybe Apple devices make volume management easier than other manufacturers?), but perhaps more importantly, isn't the site just feeding your browser a link to a 3rd-party stream?

In other words, I doubt the site _could_ do anything about the volume.