I'd get yourself
Glyph of Savagery. Use SR as you approach a mob, 12s should be enough to kill it. Rinse and repeat. Remember that you can use CP left over on a target after it's dead to cast CR too. At max level you'll want to keep SR up 100% of the time while damaging mobs. Better to get into the habit of maintaining now. I'd probably Rake mobs too, because FB has 25% increased crit chance on a bleeding target. For anything that'll be alive longer than 10-15 seconds I'd get a 5cp rip up as quickly as possible, preferably with the Tigers Fury buff.
On heirloom weapons: because they scale up every level, they often end up being significantly better than what you might find via quests, since you don't often get a new weapon every level and can sometimes be stuck with one for quite some time. The damage values on your weapon contribute heavily to your overall damage. Ask your friend to link his heirloom at his current level and compare the damage values and DPS to yours.
One last thing to note is that below max level, the classes aren't very well balanced. It's just not an area of priority for the developers. some classes also fare better than others when killing low-HP, short-lived mobs.