So, to boil all this down to the most important part,
I'm right.
Well, no, not unless you accept JMS's interpretation of events to be true. We know that JMS submitted his series bible to Paramount several years before DS9 or Babylon 5 made it to air, but Paramount is a big company and there is no proof (that I'm aware of) that Rick Berman or Michael Piller read, or even knew about, that bible. They say that Paramount came to them asking for another Trek spin-off show, but they didn't want to do two starship based shows at the same time, so they decided to either do a space-station show or a show set on a colony. Originally, they were leaning towards doing the colony-based show, and there's even some early sketches of what the colony might have looked like on the DVD special features, but in the end they settled on doing it on a space station because they wanted to film it in a controlled environment rather doing a lot of location shooting.
As for his claims that the rest of the show was similar, I don't see it. There are similarities, but there's also a lot of differences, and there's even situations where the DS9 writers introduced elements that B5 did later, such as the introduction of the small, fast and powerful warship Defiant/White Star. And at the end of the day, the characters are quite different and go on unique journeys, and since DS9 and B5 are both character shows as much as they are action-adventure shows, they are quite different. I like them both for what they are, preferring DS9 because I watched it at an earlier age.