Well yes, if you choose to ignore what the text says it's quite easy to make abilities horribly overpowered. I'll see your GFB and raise you double sneak attack. You only get one sneak attack per turn, but this is only one sneak attack - it just happens to hit two targets....but when you can use -5/+10 it get new dimension of use. And perfectly match with idea brutal power warrior. With one swing get down 2 enemies (ok like goblins, or wolfs)... 1d10+10 is dmg you cant ignore. And if you take green flame blade You are 2 target destroyer but it's really situational.