McGrath did fine even against SA. He averages 27.33. That's not bad enough to be not rated. He was even better in SA, which you would have watched more, by averaging 23.62. If this was the criterion to impress you then I don't know why you will not rate him and at the same time rate other like Wasim, Waqar etc.
I was putting McGrath ahead of Wasim by mistake in 90's list. But over all, you couldn't have been more impressed with Wasim who averages 39 in SA and 29 over all against SA.
You seems to rate Waqar as well. If you think McGrath was ordinary against SA then what do you make of Waqar's records against SA over all and in SA? He was averaging 28+ in both case.