Well Hollywood is notorious for competing films coming out at roughly the same time with similar themes.
Armageddon vs Deep Impact
Olympus Has Fallen vs White House Down
A space station based ST was the next logical step for the franchise. Besides in many respects B5 owes it's existance to ST esp. TNG. Had that not been a success I doubt B5 would have seen the light of day.
But I enjoyed both B5 and DSN.