Well, like I said, I try to look not at the wording but at the intent behind a stunt. Most of the times, it solves the issues. The rules state pretty clearly, what a stunt can and can't do, if it is doing more than that, it should be dialled down to a version where it would work as intended.
Example:
In the case of Off-Hand Weapon Training, I look at the table of what weapon ratings the author feels one handed melee weapons should have. That is effectively 1 or 2. A weapon:3 would already be a two handed weapon. If you then look at the stunt again, it gives you half the weapon rating rounded up, which in both cases (weapon 1 or 2) would be a +1 weapon rating. That means, the stunt could also be worded "grants +1 weapon rating when attacking with both a main and off-hand weapon.", which would make it fit perfectly into the stunt rules. The only situation it would not apply like that, would be when someone was attacking with 2 twohanded weapons and supernatural strength or hulking size, that would become a +2 bonus by the original wording, which might or might not be granted on a case by case basis, but since hulking size and strength already provide much additional stress, that 1 point is not going to make a big difference.
If in the game there still comes a situation, where a stunt (alone or in combination with a power) would cause problems, I would simply look at what the stunt should do at the most. So if the wording of the stunt would provide the character with a +3 on a maneuver, I'd reduce that to the +2 it should be. More than +1 on an attack? Same thing.