I started a DS9 rewatch a month or two ago (and should really get back to it), and came to the realization/conclusion that this whole perceived 'rivalry' between the two series - insofar as one being a rip-off of the other is concerned -is incredibly overblown. I am saying this as someone who loves both series. Here's why this whole rivalry is overblown:
The entire basic premise of the two series are completely different.
Babylon 5 is, at its core, about the Shadow War, with the developments involving Sinclair and later Sheridan being portrayed as quasi-spiritual figures are elements
of that premise.
Conversely, Sisko's status as the Emissary IS DS9's premise; everything that happens in the series - including the Dominion War - flows on from and pivots off of that from the get-go.
Yes, both series have similarities when it comes to their settings, certain character names, and certain thematic plot elements, but, at their core, are entirely different series despite what some - including JMS himself - might believe and/or claim.