Distributor Phasing Question

There have been discussions (and arguments) about how the distributor rotor moves when mechanical and vacuum advance are applied. The understanding is that mechanical advance does not change where the rotor is (rel. to post) when the spark fires. That is because the weights change the angle between the rotor and drive shaft. Vacuum advance does shift rotor position, but is mild enough (15 deg max) that the rotor tip stays close enough to the post to not cause a phasing problem.

My question is what happens if you lock out the mechanical advance and use an electronic controller (like MSD) to apply the rpm advance? It seems that could lead to a severe rotor mis-phase, since then the rotor would shift >30 deg. The spark might then jump to the wrong post. Below is from an RB electronic distributor currently on ebay:

"The mechanical advance has been 'LOCKED' (tack welded) for use with and to be controlled by after market digital ignition systems that allow for adjustable ignition timing curves."

My guess is you might get it to work for drag racing only, if you adjust it so the phasing is close at high rpm (not easy), then just never try to idle the engine. Most big cam engines barely idle anyway.