I wonder how much of Franklin's arc was recycled from Dr. Kyle's planned arc? "The Gathering" establishes Kyle as a stim user; which was basically transferred directly to Franklin and his story arc with the stim abuse.

At the end of "The Gathering" Kyle seems downright in shock after having seen a Vorlon when he opened Kosh's encounter suit. He even talks about how seeing a Vorlon is a life changing experience. If Kyle had stayed with the show would he have been the voice of skepticism in the face of religious/spiritual ideas that Franklin was?

***SPOILERS AHEAD****

Finding out that the angelic figures from your world's religious texts are Vorlons would be a big shock to anyone's faith. We later find out that the Vorlons did guide the younger races and that stories of encounters with angelic beings were Vorlons appearing to them.

It would certainly add a new layer to Franklin's argument with Sinclair in "Believers." Sinclair is a religious man and asks Stephen "what if God doesn't care how you say your prayers just as long as you say them?" Stephen responds "what if there is no God?" It would certainly add another layer of depth to that conversation if we later find out that the doctor already knows that Vorlons are the angels from our religions. But because of patient confidentiality he'd be unable to answer Sinclair's question by saying "I've seen the face of an angel and it's a dam Vorlon."