Even though the producers had to keep the show relatively episodic, you'd think by this point it wouldn't be too much to throw a scene or two detailing this build-up to the invasion in the episodes prior.
I'd like to think that this is the result of interference from on high, but I suspect it's just the result of the writers not thinking things through in advance. Other than the designated arc episodes, they seemed to approach each episode as its own story, just like they learned to do on TNG. This is definitely one area where Babylon 5 outshines DS9. The shows are pretty evenly matched in my opinion, but B5 always kept sight of the grand plan while DS9 kept losing track of it.
According to Ron Moore
It's an interesting tidbit that Kira takes command of the Defiant, rather than Worf, who we have usually seen commanding the Defiant in Sisko's absence.
Probably it's partly the writer's desire to reinforce Kira's command role again here at the end of the show, as it had really lost prominence in the middle seasons.
, it was a last minute change and they goofed it up:
Ronald Donald Moore wrote:
Of course, the real reason was that we came up with this whole beat relatively late in the game. In fact, the scenes in question were on the stage and being rehearsed when we decided to play Sisko as feeling so incapacitated by what happened to the prophets that he needed to leave the Bridge. Kira hadn't had much to do in the show and we thought she'd do a good job of stepping into the breach. To be honest, the Worf question never came up in the extremely limited time frame everyone was working under.
But I think that ties in nicely with what you were saying about the writers losing track of the characters. They can't even remember who the XO of the Defiant is at this point, they must really have needed to sit back and refresh their batteries.