Yes, slotting the bearing or opening allows more time to fill.
But, higher centrifugal pressure at higher revs means the same oil supply doesn't last as long. If the rod passage is critically low on oil (or out) as the critical period approaches (nearing TDC or after it when major loads are applied) then it's a bigger problem than running out when there's no or light loads (passing bdc and coming back up). If high pressure oil is fed into the crank passage right around TDC, then there's always oil there at the right time, even if it runs out later.
