Have you ever looked at a Nuke script of an artist who really knows how to key. Have you ever looked at the script and said "Where's the matte". An artist who comes to mind is Brian Begun. He is an amazing compositor and really knows about keying.
I think most keying is taught by the wrong method. I believe most artists think that Primatte is a way of keying. Granted Primatte does have it's own math which makes it different to say Keylight, and vis versa. Primate is a companies take on a certain kind of keying. In this case color difference keying. What's lost in the this is people think that's how you key. When I mean key I mean a way to place A or B. When a greenscreen comes across your desk your thinking IBK, or Keylight. Maybe some tricks thrown in for edge work. But when presented with a shot that has no screen. That's we're the real matte creation begins.
One of thing things Mr. Begun taught me is; place A over B with a merge and play with the settings. You might get something. Only pay attention to the edges. The core matte can be made in anyway you can.
Making a key isn't a node or effect. It's math. Sorry.