That was a rather disappointing episode. Garth turned out to have been bitten by a werewolf and became a member of a cult of lycanthropes. Garth's "stepmother-in-law" was the villain of the story, and the brothers Winchester hardly lifted a finger to defeat her. More brotherly drama ensued. Stay tuned for next week's episode ...
You just described half the episodes of Supernatural.
If the Winchesters were such a threat, why wouldn't the monsters ever just kill them straight up? Don't push them against a wall (considering all these creatures can do, pushing humans against the wall is like their go to move), don't tie them up and talk to them for 10 minutes.
Although they should be braindead by now, with all the concussions they've gotten.