Ugh, in re-reading that I realize that I contradict myself on the bit regarding Whedon. I meant to say, that while Whedon was fairly involved in the writing of Seasons 1, 4 and 5, he was not "that" involved in the series as a whole. He left most of it to Minear and Greenwalt.
Minear left at the end of 4, so Whedon pinch-hitted or assisted Jeffrey Bell who was the new show-runner. And Greenwalt left at the end of 3 - and Whedon came in to help "fix" the series a bit with Minear. In one - he was involved to the extent Greenwalt needed him to get things started.