[ISilenceI]

Undergeared is relative. You'll know if you start tanking a boss and you are unable to keep threat with the long combo. This doesn't happen often. Usually only when the rest of the group is far more geared than you are as tank.

The profiles have built in threat loss combos, so if you lose threat, it will automatically stop using the long combo, but will go back to using it once you have threat again.
Even though it does this, we all know losing threat on a boss for even a few seconds can result in a wipe.

All this being said, I have yet to lose threat on a boss with the long combo.
Above situations are entirely hypothetical.