A bit late now as the pump is off, but leaving the bike to stand, oil tank full, sump plate off and timing cover removed would have allowed any leakage other than internally via pump and bearings to be observed.
Failed pump gasket, loose pump, hairline cracks, poor mating surfaces and porous, failing pump body would be things to look for, plus leakage from the pump drive spindle....there is no oil seal on these pumps. It looks to be draining down pretty quickly on just standing, more than expected.
With the pump off, the anti wet sump ball valve can be felt with a matchstick pushed drown the oil hole closest to the timing bush..... You should feel the ball move and return under light spring pressure. Treat it to a dose of carb cleaner. Failure here allows drain down, so stuck open or you may find it has even been removed. That explains emptying of the oil tank on standing..... But not the poor return.
Flow and return are metered by the differing pumping capacities of the supply and scavenge circuits, but only if all oil goes through the pump. So bypassing the pump on the supply side overwhelms the scavenge side and all the oil ends up in the sump.. ... as does any failure to scavenge.
Swarfy.