Heroics are is the place to gear up unless you expect some to run thru all the previous raids to gear up, and in that case you should take the time out of your busy busy day to run them thru those raids as many times as it takes to gear them.. Oh but wait, since you dont have an extra 5 minutes to waste in a heroic you dont have time to runs those same people thru the older raids.
It's called a group effort people. The tank is in charge, let him pull unless you can solo the place without stopping to heal yourself. If you severely out gear the tank, so be it. That gives you no right to pull for him unless you think pulling raid bosses before the tanks is a good thing.
Yes the tank should be trying to keep aggro on the whole pack of mobs instead of just one or 2, and the tank has to learn how to do that properly. It would be preferable for that tank to learn to do so with a guild group if it's their first tank.
In short, don't pull before the tank EVER!. It is not your job. If you are so constrained on time that you have to finish a 20 minute instance in 15 minutes then maybe you should wait til you have a lil bit more time.