With regards to Martial Arts in SC2.0, your base untrained unarmed damage is 1D3, if trained 1D4, with the Martial Arts Feat it goes to 1D6+the stat bonus, and if Master's Art then you are at 2D6+the stat bonus. With Master's Art, you do have a threat range of 18-20. It is not overpowering considering what you are spending to get it.
I agree that you should get something awesome when you sink that many feats into one thing. I disagree that better threat and more damage is awesome from anything but a "winning the combat minigame" perspective.
As for the Disarm vs attacking choice, I chose to attack because I was betting that I had a better chance to crit with a 18-20 threat range than the skill check threat of 20. Plus I could deliver 2D6+3 in damage and if it was crit then I could do 15 Wounds, not counting any additional AD to damage, which would drop my opponent. It had nothing to do with the Disarm action being less effective because of the action itself.
I still feel like you're making my argument for me. I argued that all of the special maneuvers aren't as good because they don't tick down the vitality clock, and you confirm that a 15% probability crit and damage are the better option.
I realize I may be asking too much here, since this is after all a hit point derived game. But maybe there are alternatives.
How about this one: any combat action against a mook should have a chance to take out the mook.
Disarm? He suffers stress and/or surrenders (incidentally happens also in movies). Grappling? Maybe fatigue and knockout? (Hardly unbalanced, because you can only get one guy this turn, instead of two (or more with Cleave).)
When fighting special characters, maybe all attacks should cause some form of damage (vitality, stress, or fatigue), in addition to whatever special effects they produce. That way, you always
tick down the clock, and don't feel like your attempts aren't leading anywhere.