Eric, I agree with what you are saying, but, the whole flywheel, crank and pulley (lightened or OEM) assembly can be balanced outside of the engine. However, when it's installed and utilized it's becomes unbalanced again. The clutch wears down the flywheel somewhat irregularly and the accessory belt(s) when tensioned, apply an uneven amount pressure on the other end.

To your point about 1st, 2nd and 3rd order harmonics, if an OEM manufacturer developed a damper to absorb harmonics that they could not eliminate internally why would we want to remove it even if an engine builder balanced the whole assembly given the caveat mentioned above?