My feeling, from 20 years of reading all the available quibbling, is this: jms presented his presentation to paramount. Paramount turned him away, but said to themselves "This is really a pretty good format. Let's develop something along those lines but put it in our Trek franchise universe." So you got the basic setup of the Casablanca-like atmosphere on a space station near a wormhole/jumpgate. Maybe
some of the character beats were lifted or inspired from jms' treatment, with some changes to fit into the Trek universe.
Then once the show got started, the two diverged into their own things and went, mostly their separate ways.
Maybe B5 liked the defiant and came up with the White Star.
Maybe (probably) DS9 saw how cool the Shadow War idea was, and worked the Dominion War up.
As has been said, show biz ain't averse to borrowing from each other.
And just to be clear that I'm not trying to tweak the fight or troll or anything - I emphasize and reiterate that I still love both shows dearly, and I'm glad we got them both.