Season 5 got royally screwed by real life.
First, the network canceled the show midway through season 4. So the writers scrambled to jam in all of the important plot points in the last half of 4. Then the show was unexpectedly un-canceled, leaving them with very little to do for 5, so they had to gin up some kind of a plot to fill in the gaps. Thus the telepath rebellion.
And then, there was some kind of miscommunication which resulted in Claudia Christian leaving unexpectedly. No one seems real clear on exactly what happened, but it doesn't seem to have been what either Claudia or JMS would have wanted. However, it happened. Thus, Ivanova out, Lochley in.
Writer, not writers. Seasons 3 and 4 of Babylon 5 were all written solely by JMS, as was almost all of season 5 (with the exception of the episode Neil Gaiman wrote). As JMS tells it, the original plan was to end season 4 with Intersections in Real Time (the episode where he has been captured by Earthforce and they're trying to break him via interrogation), and to have the liberation of Earth happen in episode 6ish of season 5 (much like the Shadow War ended with episode 6 in season 4). This means that season 5 had to be extended by about six episodes to make up for that.
As for Ivanova, JMS's explanation at the time was that it went something like this: since the show had technically been canceled, so had the contracts. Time was of the essence, so they asked everyone to sign up again with the old contracts, and I'm assuming there was some automatic raise going into that as there usually is in TV. Christian was looking to get into more movies and/or other things, and wanted a contract for fewer episodes and/or a guarantee to be able to take some time off, but at the same time wanted to be paid the same. That wasn't acceptable, and because there really wasn't any time to negotiate they cut her out of season 5.
Originally, part of Lyta's season 5 arc would have been Ivanova's. She was the one who was supposed to fall in love with Byron, for example (perhaps spurred on by Marcus's sacrifice, as a "life's too short" thing).
I haven't heard of Intergalactic; another one that everyone wanted to go on longer was Stargate Universe, which I liked, except I see why it failed, as it was not the Stargate everyone was used too, much darker in tone, and a serial, not episodic.
Stargate Universe very much felt to me like someone had seen the BSG remake and went "Can't we do that, but in Stargate?"
As for serial versus episodic, I'm going to ask Loki what he thinks of that:
For me, the ideal structure is that we see in most of Babylon 5, as well as Stargate SG-1, Buffy, Angel, Farscape, and Deep Space 9: individual episodes that tell their own story to completion while also contributing to an overall narrative. For example, the season 1 Babylon 5 episode Mind War is about a telepath that's been enhanced to dangerous levels threatening the station with his uncontrollable abilities, and the episode ends with Sinclair letting the telepath go away in a shuttle or a Starfury and become some sort of energy being. But at the same time, it establishes the character of Bester, and Talia's abilities start increasing which will be relevant in later episodes. It also establishes Catherine Sakai as Sinclair's sometime love interest. We also see the Walkers at Sigma 957, and we get to see G'Kar rescuing Sakai from the aftereffects of their visit which shows that he's not all villain as he had been previously presented.
That's the kind of storytelling we rarely see anymore, because most shows have become
too serialized. They all become a single narrative, with no opportunity for character development or for letting the plot breathe.
