They didn't actually fight off a Klingon fleet. They held their own against it long enough for the Klingons to consider it cost prohibitive to stay there until the Starfleet reinforcements arrived, especially as they already had a war with the Cardassians.
Likewise, I'm sure DS9 would have given the Borg one heck of a fight, and even held out long enough for a fleet to arrive. But if that fleet isn't coming? Well, they'd lose.
Likewise, I'm sure DS9 would have given the Borg one heck of a fight, and even held out long enough for a fleet to arrive. But if that fleet isn't coming? Well, they'd lose.