Requested oiling mod info

Allow me a stupid question. Wouldn't grooving the rear most camshaft journal or using a grooved rear camshaft bearing provide full time oiling to the top? I know it does on a slant 6. And since the oil pressure essentially comes from the bottom end, HOW exactly do you get full time oil to the top without taking it from the bottom? Not arguing, just trying to understand. Thank you drive through.
The cam journals are stealing oil from the mains when they send the pressure up top, fully grooving the cam would make that dynamic worse.