Can we hold A mob easy... yes.
Can we hold MANY mobs easy:
-Vs single DPS'd mob... yes
-Vs AoE DPS... no (I can't anyway... but that's a post I see typing in the future)
Your post really does not tell the story of your friend ripping hate off you.
I'm guessing he's a Rogue or Shammy. I'm guessing he opened with a high threat ability or spell (ambush and shock), even before you could get 1 maybe 2 Sunders off.
Thanks to the mob not facing you, you're not getting much rage from taking damage, which is starving you of rage, so not all the abilities you would like to use.
Meanwhile, your DPS buddy is constantly laying on the DPS, helping his Epeen grow on how he can rip hate off the tank.
God, I'm glad I have not been in a party like that lately lol. DPS tend to do that man. If it's a huge problem, like they're dying tell them to chill. If they're not dying, just keep doing the best you can.
Early levels I'm guessing you're not Protect spec'd. You don't have Defiance yet (and should not need until much later).
There's only so much you can do other than Taunt, Sunder, Challenging shout, Mocking blow (later on Concus blow will stun the mob keeping the DPS safe until Taunt is ready again).
The DPS needs to understand you're like a train. It's slow starting, but ones you get up to speed (with rage) you're hard to stop (err... pull threat from). That's why I hate when Hunters leave Growl on. I need dem rage points. If I'm figthing a Growling pet 80% of the fight the mob is not attacking me 50% of the fight.
Meh, stick with it OP. Tell him to calm down on the dps explosion.