There are similar stories about Babylon 5 (envisioned as a 5 year cohesive story arc; lots of changes to the plot happened over the years of production)
This really shouldn't be too surprising to anyone who has worked on a creative project over an extended period of time. Heck, NaNoWriMo has you write a novel in a single month and I doubt many people have the novel hit exactly all the plot points they had originally thought up. How much more should we expect plans to change over many years (and with external constraints).
To be fair Babylon 5 WAS planned for the 5 Season Arc and only extended after the original plans for season 3-5 were essentially compressed into what became season 3 and 4. But from what I know it's true that the Babylon 5 we got was substantially different from the one originally planned. Here's a very detailed Discussion of the original story line https://www.trekbbs.com/threads/synopsis-of-jmss-synopsis-of...
I don't think 3 was compressed, it was 4 and 5 that became 4 due to fears the network would cancel it without having a chance to resolve the big arcs. But even there, the story was that they did it by dropping the side plots, and then the 5th season that aired was made entirely of those dropped side plots, not just extended in the usual sense.
Also interestingly from that link, the end of that version of season 5 where Sinclair was believed to be a traitor, got rolled into the planned plot of the Crusade spinoff, though the series was canceled before they reached that point.
This really shouldn't be too surprising to anyone who has worked on a creative project over an extended period of time. Heck, NaNoWriMo has you write a novel in a single month and I doubt many people have the novel hit exactly all the plot points they had originally thought up. How much more should we expect plans to change over many years (and with external constraints).