That's an interesting analysis, thank you, but I'm not sure how much of the problem is due to the deficiency of IRV and how much is due to other idiosyncratic features of the Australian political scene (such as the influence of Murdoch media, or even the policy of mandatory voting).

In any case, fortunately there are better options out there than IRV, even with the requirement that districts don't change size. One popular (and simple) option is Approval Voting, although it is slightly harder to count than plurality (at least by hand, since you need to separate ballots into potentially 2^n piles, for n candidates).

The alternative I'd recommend is Asset Voting, where the ballots, districts, and counting remain the same, but after the count is complete, the losing candidates (from least popular to most) get to reassign their votes to other candidates until one of them has over 50%.