340 Oil Priming Question First Start

Best way I can think of to kill a cam. Or the bearings or bushings in roller lifters.

It’s pretty simple to turn the engine by hand to get oil up top.

Laying on the starter to do it is asking for cam failure.
Just trying to learn. Why is this so much worse than hand priming? Is it the initial movement not having oiling? If the oil pump is primed shouldn’t that oil flow right away?