'DS9 stole a lot from B5', I would not say 'stole' exactly, because that word is very loaded but certain developers and writers borrowed heavily from the original JMS script. As the seasons moved on Babylon may have lifted ds9 ideas or borrowed back, taking DS9 arcs and concepts and making it their own.
I wrote on this a long time ago
Was B5 brought to Paramount?
Yes, it was, and I have the correspondence to prove it. Were some of the
development people at Paramount who read the B5 screenplay and saw the series treatment and bible also involved in the DS9 development? It seems that this is indeed the case. That's not unsubstantiated "bs" as you say, and I really don't care what you think on that subject. All of that is a matter of record.
Were Pillar and Berman aware of B5 at any time? No. Of that I am also confident. The only question in my mind is to what degree did the development people steer them?
If you use that logic then any show with a starship with over a hundred people on it and travel faster than light should credit Gene Roddenberry.
In online interviews Walter Koenig (Pavel Chekov, Bester) often talked about the freshness and originality of the B5 show, now why would a legend like Keonig who was always dedicated to Trek keep saying something like this ? Let's look at some of the other connections, both wanted charming characters but very different to Gene Roddenberry's original Star Trek vision and because war, terrorism, poverty etc feature so often in DS9 and its tone is totally unlike the other StarTrek's it is refered to the black sheep of the Star Trek family, the only problem being B5 came first. Deep Space Nine was not announced by Paramount until long after the announcement of B5 by Warner Bros. Both DS9 and B5 had spiritual beings enigmatic god like people, the Vorlons, the Prophets. B5 and DS9 both had shape shifters, and the two doctors from both shows had hidden secrets. Bashir had his genetic enhancement and Franklin's involvement with the underground. Other possible links Jeffrey Sinclair a war vet while DS9 had Sisko veteran of the fight at Wolf 359, the commander of each station eventually became a religious figure....I believe as Babylon-5 moved on - the tide started to turn the other way and the B5 people began to think if you can't beat them join them. This might be why Babylon-5 then started to borrow DS-9 ideas such as the allegation that the Whitestar was DS9 inspired since DS9's Defiant came first.
The difference between the people behind both shows, is that JMS and other B5 people seem to have no qualms about giving credit to Star Trek, Dune etc and how they inspired JMS and his work etc but Wolfe, Moore and the people are Paramount only get all emotional when the B5 connection is brought up and IMO this only adds more fuel to the theory a lot of borrowing was going on.