Oil (or any fluid or gas) will always move and flow to a lower pressure area. This is the basis of aircraft lift and how an internal combustion engine intake cycle draws in air. Atmospheric pressure is flowing into the lower pressure cyclinders (intake vacuum). Oil will flow to both the crank and cam/head but the majority is flowing to the head since it has more leakage. If the head had a true open oil bleed, say you lost a rocker shaft plug, then the pressure drop at #4 would be even greater, lowering the available pressure going to #4.
The oil flowing in the galley at #4 also feeds the one head. This induces a local pressure drop at the intersection of the#4 crank feed and the cam and head. Mopar designed the cam and head to only be fed part-time. Increasing the flow to full-time with a grooved cam journal or rockers that bleed more oil than stock will further reduce the pressure seen at #4 crank. This could explain your 2 and 4 crank failure, possibly from starvation. Or at least, play a part if oil starvation was the root cause of failure.
High volume pumps are great and they can really work on an engine that has a lot of oil bleeds from large bearing clearances, an oil cooler, turbo, some aftermarket rockers, etc. They only work if you have some of those mods/parts. Otherwise they're just bypassing the excess you're not using to maintain safe pressures. They offer the same pressures as a normal pump but can keep up with extra bleeds whereas a normal pump couldn't.
