I was thinking;
the oil pressure is measured at the top of the main line. It is not measured at the pump.
So; what if the pump was running super high pressure, and dumping at the bypass, because there was a restriction up the line. But as soon as the oil got thru the restriction, now the system is regulated by bearing leakages and so on. Boy-O-boy that pump could be working overtime.
The only place I can see such a restriction occurring is at that diverter/separator cup-plug that is driven vertically up the main line to divert oil to the filter. Unfortunately, the oil-pump has to come off to inspect that cup.