I used to run a lightened flywheel on my drag cars. It allows the vehicle to rap faster. Better throttle response. Thats nice on the street but when climbing rocks, smoother is better. On a big engine you can get away with a lighter flywheel because you have more hp and torque as well as more cylinders firing per revolution. With a 4 banger it is a long time between cylinder firing at low rpm's. That is why the 4 banger tends to buck and stall. The inertia ring in scientific terms, integrates the energy. In other words the power is stored in the flywheel between cylinder firings to be used to continue the rotation of the engine and to drive the wheels. Most speed shops don't understand the physics of rock CRAWLING, and try to apply high rpm physics.
Forget the physics.......it works better, period. Check out the yahoo stroker forum. Even with the 6 cylinder stroker, it is recommeded to get the older heavier crank to aid in low rpm torque. Yes you don't have the fine throttle response, but try lugging you 4 banger with an aluminum flywheel at 400rpm.
Unless the person you talk to is a rock crawler, take what they say with a grain of salt.
Tom Houston