Blade of the Resistance is definitely overpowered. +2 to damage against nearly any opponent as a free background feat goes beyond the very limited scope that background feats exist to fill in 4e. Compare to any of the background feats in PHB2, or Scales of War, or Forgotten Realms. I have yet to see a background feat this powerful.
That said, I'm completely with Morrus and RangerWickett on this.
Morrus said:
We've not found it unbalancing anything, and we're into Paragon now.
He didn't say anything about it being overpowered or not, which, at the risk of putting words in your mouth, is what I think you're really driving at.
Several of my players took this feat as well, and I hesitated allowing it, but with the mindset that its a tasteful, fun feat, I did so and it's paid off: when a player uses it in the heat of battle, particularly when fighting Ragesians, it tends to highlight the character's anger and aggression towards the targetted party.
The +2 to damage, while mechanically overpowered, does not affect our game in any meaningful way. As with most rules, your experience may vary, of course -- but there are better courses of action than simply banning the feat. For example, consider selecting the target of the extra damage to be a minor action, or even a standard. Players may hesitate to take it then, but at least you're not forcing them to avoid taking feats that are in the Player's Guide.
Another way to balance it would be to make it a daily power. None of this is necessary in my game because it's not unbalancing.
Regarding monks, we had a player who was a monk in Gate Pass, studying abroad, as it were. It worked out quite well. Considering the Monastery of the Two Winds is a major part of the campaign world, and with all the information RangerWickett provided above, I think a monk character is one of the best ways to add some flavor to a character in Burning Sky.
I'm starting #4 (Banquet) now, and so far I haven't seen any instance where having a monk would be troublesome.