Two different criteria though. WI were the best team of Imran's time, but India were no where near the best in Warne's. Personally, Warne struggled v India but they weren't, until say between 02-04, realistically pressing for top spot. Warne won plenty of tests for Australia, just as Imran did for Pakistan.
It's no surprise players have their sides they do better against. WI were still number one in 93 (they'd just beaten Aus in Aus) yet players like, say, Robin Smith or Alec Stewart scored more hundreds v WI than Australia.
But I would agree Imran as a total package was a better cricketer than Warne. I just don't accept that particular reason you've given there as the basis for saying so
.