First of all - it's a paid ability. And its in Tactics, a sphere with 0 resource acceleration.
Second of all, for it to be a "free feint", as you call it, the player must have sufficient enough threat to not engage that enemy automatically in the first place.
Third of all - removing it threat from the staging might be a decent way to go about Tactics questing, don't you think?
Fourth of all - for this "free dagger" you need to stay below the enemy in threat, which is problematic for tactics. Plus, his base attack is below average.
Pair him with Mablung, and it's a free ability.
Pair him with hobbits, and you should be fine. And against high engagement enemies, he is too good.
Agreed, but not as a cheap, repeatable hero action. Westfold outrider is a good example of an appropriate cost.
Pair with hobbits, or don't run mono-tactics. No one said you have to run the shadow with Tactics Aragorn and Beorn.