Just because you can get oil out of the 'dry' sump on an oil change, doesn't mean the scavenge pump has inadequate capacity. Firstly, the scavenge pump doesn't empty the dry sump, it merely pumps to the point where the mix of oil and air drawn in balances the flow of the pressure pump. Secondly, when the engine is stopped oil drains back from the tank to the sump through the scavenge pump.