In theory it seems a good idea, sometimes in practice it is the other way round. It can be useful to force a sudden change in weight transfer across the axle in limit handling events.
Any geo engineering project will create winners and losers. An example of this is cloud seeding, which has threatened to start wars in SE Asia, and in Tasmania for example is used to increase rainfall in the catchment for the hydro dams, at the expense of causing reduced rainfall in the...
Professionals design springs for road use such that they have a minimum preload of X with the wheels at full droop, ie on a 2 post hoist. Amateurs don't, they worry about powder coating.
In theory it doesn't matter where the trial weights are located on each plane relative to the other plane, I think. But i haven't done this in a long time(25 years). I'd have thought so long as all measurements and locations were referenced to a single shaft reference marker it would be OK.
You do the 2 single plane balances by record the vibration or velocity at both planes. Same number of runs just more data.
Maths is here https://www.eng-tips.com/threads/diy-crankshaft-balancing-with-an-oscilloscope.511892/#post-8933361
Frankly I'd be calling in a large motor balancing guy.
Did you 2 plane balance? Since automotive crankshafts are oil bearings I don't remember any problems balancing them.
Depending on the natural frequencies of the rotor you may be operating above the whirl speed. Certainly possible...