I agree, Holt, McEwen, Gorton wouldn't matter. The Libs still had the public support overall. McMahon was an AWFUL PM (great treasurer)... but literally anyone could have beaten him. But the "It's Time" campaign was one of the best political campaigns EVER... right up there w/ Morning in America for Reagan.
Holt vs. Whitlam in 1972 *would* be quite a different matter to '69. I'd actually give Whitlam a bigger win over Holt; the Vietnam stain on him would be large and smelly. That said, there were other issues.
Also, I love the 'it's time' campaign too.