What results? What actual evidence is there aside from what some players think happens?
Not every point of view has a thorough documented scientific experiment to support it.
My results, many friends results, many people in my pool hall results. Maybe it is all psychosomatic or maybe there is some physical explanation. A combination shaft thickness, tip size, tip shape, when in the hands of imperfect human beings, results in repeatable differences. Could be affects of closed bridge looseness, shaft shifting/offset when using english, contact point not where intended, etc..
Is it your opinion that a beginner player will pocket the same with a 13mm shaft with nickel shaped tip vs an 11mm shaft with dime tip ?