Well I set up a situation.
Three populated systems are threatened.
Between them and the Jem' Hadar ships around 600 total, is a rift that could slow the Fleet down. The rift is a discharging nebula fillament. The Fleet can't go through all at once and they'll exit at multiple bottle necks.
Sisko or Kira would have to negoiate the expanse faster and get to the systems first and rally their limited forces to catch the Jem' Hadar at 3 crucial bottle necks.
Problem is the governments in the three systems don't get along very well. Two of the leaders have very strong differences and might just firing on each other rather than the Jem'Hadar. The Heroes have to coordinate the natives to protect sectors that potentially would shield a government they hate from the Jem'Hadar fleet. If they get it wrong the natives might let the fleet through or not put up enough of a fight against the Jem'Hadar vessels.
Meanwhile Defiant has to slow the Fleet down and reduce their numbers so the Allies can handle them. Star Fleet has dispatched a fuel ship and a rearmor vessel to out fit Defiant with Additional torpedos and Phaser coils. Other than that Defiant is alone. And once the supplies are gone there is no more and help is over 1,500 lightyears away.
This story would litterally be like Defiant alone (almost alone) going at the Dominion Fleet at Sacrifice of Angels.