You are missing the whole issue.
When the mass of the counterweights is not enough to counteract the weight of the reciprocating and rotating weights, you either need to add mass to the counterweights (Mallory metal) or you need to add that mass at both ends of the crank, externally, like adding weight to the damper and flywheel.
I’ve had to add Mallory to more steel cranks than I care to remember. The cast crank, with the same size counterweight doesn’t have the same mass as a forged steel crank.
