Your greatest leveller at this point would be PvP (unless you've obtined the Kyuubi Mount); The damage calaculator may be fustrating at times, though you'll just have to be patient with your levelling. Complaining about the high damage hits would only result in an IP ban.
Note that when battling, multiple opponent confrontations could be a hassle for anyone without an active mount or AOE-Damage techniques. The opponent you're targeting is merely a scapegoat, while the others may deal twice as much as you're not focussing your attention, or defence, on these enemies.
