Agree with all your points.
Feel free to take this with a pinch of salt guys, this is not verified, just something I've heard a few times in a few different places...
Apparently Coon was Christian and GR (clearly not being one), hated the ending. Equally Coon hated the jabs at TV networks that GR wanted in there. The writing process became a tug of war, and Coon - exhausted by the goings-on well covered in this thread, decided to walk.
However it happened, his departure was a massive, massive loss for the show.