Three things to add on this topic:

All conventional piston/type engines experience harmonic resonance at some RPMs. How much and at what RPMs depends on material strength, design and other factors including cylinder pressure (which can't be replicated by a static machine shop balancing). Two engines of the same construction could experience different harmonics with different mechanical compression ratios or due to other tuning differences such as fuel mixture flow and ignition timing. The OEM may have felt a need for a damper because at the common 55mph there was a harmonic issue which you won't see in a race application. Or, your normal race RPM may be right at a problem speed.

The bottom line for your engine builder or your own determination is does a harmonic dampener free up horsepower that otherwise would have been lost to vibration and does it make the motor more durable?

The flywheel weight which was questioned is not normally as important for the harmonics because the clutch pressure plate, which is largely a giant spring, absorbs some harmonic vibration on an engine. I have seen only a very few factory motors which include a rubber isolator ring on a flywheel.