Defense is a wily beast. it comes in two versions, and I don't recall the actual names. Basically, they are damage type, and the range of the attack. (positional)
So Brawl is Melee Smashing damage. You can defend against it with either Melee Defense or Smashing Defense. The game will use whichever is higher. If you have 10% def to both Melee and Smashing, you have 10% total def against that attack, not 20%.
When this all came out is was kind of ugly because FF Defenders buffed Typed defenses (Smashing, lethal, fire, and so on) but not the ranged ones. For a Super Reflexes Scrapper, that had only the range defenses, it meant the buffs didn't stack at all.
Now, the FF def buffs affect all of the damage types (except Psi) AND the range defenses.
With MOG, you get very high defense against all damage types (except Psi), but nothing for the positional (that's the name) part of the attack. As far as I know, this is by design. If it buffed the positional defenses as well, any psi attack that had a Positional tag assigned would be affected by the power, and that's against the design of it.
If your Brute is a Broad Sword or Titan Weapon, or anything with a def buff that buffs Melee Defense, it will also buff Smashing or Lethal, or whatever, but it will do one of each. The damage Type will stack with MOG, but the Positional will not.