This is somewhat true, and something I believed as well. Until I took a look at their stats in victories. Not a deep dive by any means, but for me interesting.
Warne
92 wins - 27 5fers - 7 10fers
McGrath
84 wins - 18 5fer - 3 10fers
And just for comparison
Marshall
43 wins - 17 5fers - 4 10fers
so Warne seemed to sometimes be more of a driving force in wins, even if slightly. But yes, could also be after McGrath took out the openers
Marshall though, in about half the wins had one less 5 wicket haul and one more 10 wicket haul.
these are the little reasons btw.