I have a theory about things going wrong with crankshafts with lightweight ignitions. It has to do with Torsional Vibration.
By swapping the stock flywheel for the much lighter mini-rotor ignition, there is greatly reduced inertial dampening on the ignition side of the crank. You also have the force impulses from the piston/combustion increasing in both frequency and amplitude due to your more powerful and higher RPM setups.
Every time you get a pulse from the cylinder, you are winding/twisting up the crankshaft in between the clutch side and the crank cheeks like a torsional spring. Then it unwinds. Back and forth. At 10,000+ rpm. When you lighten the ignition side, you take away dampening and create a more asymmetric reaction on each end of the crankshaft.
I deal with this on propeller shaft installations on boats. For every boat we design we have an outside company evaluate all the components in the drive train (Propeller, Shaft, Engine, PTO Items, Etc.) They look at the engine impulses driving everything as a system of torsional springs. Looking for harmonics especially. There is a lot of Finite Element Analysis and I only read the reports, but we just had a boat that we had to add a mass disk to, for this very reason. Without it they were predicting that we would have destroyed the drive shaft in no time.
My prescription, add rotational mass back to the ignition. It's not weight, it has to do with rotational inertia. You may not have to add all of it back.