I didn’t say or imply that it’s not internally balanced. Most engines we come into contact with are internally balanced. We even up the piston and rod weights and balance the crank and rods. Then the internal rotating assembly is balanced as a whole (if customer requests it). Then the damper and clutch/flywheel are individually balanced (not attached to internal assembly) if the customer requests it. They don’t need to be attached to the internal assembly during balancing because the internal assembly has already been balanced.
As you well know, when you balance the internal assembly and then bolt a damper or clutch/flywheel assembly on which is out of balance, the system becomes imbalanced and that’s what we all want to avoid.