I don’t really see how the standard basic Sentinels have a chance against Dark Watch. They don’t have the experience to compare to Fixer or Expatriette or the sheer power of the magic of Nightmist (or presumably Harpy).
We are comparing here characters who have 4 full decks compared to a team that aren’t strong enough to have their own decks (until void guard). The fluff backs it up too I think, this is one seriously one sided battle. Medico doesn’t have the attacking power, Idealist doesn’t have the defense, Mainstay can tank for a bit but that won’t keep them going for long, and is outclassed in survivability by Setback. Out of all of them Writhe is the most difficult to quantify I think, but that’s then only one man still.
The biggest threats to Dark Watch aren’t the Sentinels but are more likely to be Setback or any fall out from Nightmist’s/Harpy’s magic.