I'm ranked #8 on that fight, and execute is only 8.9% of my damage. Honestly, it seems that the worse the warrior is, the higher % damage of his is execute with some obvious exceptions (Fights such as elegon). Because less damage is being done overall, a greater proportion of damage done is execute. This may not apply to you, but some warriors (Cough fking rossi @ joystiq.) are bitching about execute because they suck at playing.