I think Maggin did the right thing with the Challengers story.
So do I, but it's too bad that he lost his job. Imagine if he was still an editor!
It seems to me that Carlin was just upset because he went behind his back.
I think Carlin got upset like that a lot. Mark Waid also used to be an editor at DC Comics, but then he let Kara Zor-El make an appearance in a post-crisis Christmas special. (It was a fantastic appearance in a great story, and as far as I know it's the only post-crisis Kara appearance other than the recent Peter David story.) Waid was fired faster than you can blink.
It was years before he did anything at DC again.