I'd imagine a hex editor for music would be like a chiptune tracker.
Pure Data's domain is digital signal processing, with an emphasis on sound. It's good for prototyping because one edits the signal graph, GUI, and event-triggered scripts in the same visual window using the same event loop.
I say idiosyncratic because when you can connect anything to anything else, weird things start to happen. (For example, adding two more boxes to the diagram to control the crossfader with the pitch of someone's voice.)
Switched to Sublime Text years ago. I just have my configuration, and it works fine for me, so no need to change it for the rest of my life. I don't even care if it's not updated ever again.
I don't know about that. I think the visual programming aspect is the most defining trait, in which case...? I don't know any general purpose non-toy visual programming languages/interfaces. Scratch exists but likening PD to Scratch doesn't seem fair to me.
My only knowledge of PD is from graphical interfaces that implement components using it, so my assumption was that Csound was lower-level due to my (brief) experience writing on it.