The episode could have been rewritten so that the DS9 characters were integral to the plot. They had the opportunity to make something really special with this episode and they sort of blew it. The episode is fine as is, but it had the potential to be so much more. Just my opinion...
With that logic, we might as well re-write every single episode that had the potential to be "so much more." It's not like the writers planned a DS9 crossover and failed. The episode was never supposed to be a DS9 crossover in the first place.
And honestly, the crew of DS9 was a lot busier with other things (like, ya know, the war). The Defiant would have had no reason to be where the Prometheus was.