I'd like to point out that Australia is still dominated by two parties even with the benefit of the parliamentary system (giving proportionate seats to other parties). This forces two major coalitions which isn't extremely different.
This is true in the lower house, but not in the upper house (the senate) where there are 5 significant parties holding seats (counting the LNP coalition as one party and the Centre Alliance as a significant party) plus some independents, and no natural majority across any combination[1].
I said "dominate" not "absolute control." I mean you're talking 14 candidates between 5 parties, with 9 from Green (5 between 4). By "dominate" I mean that the 2 parties (Coalition + Labor) control ~82%. Even America isn't 100% controlled by Dems + Repubs, but it is the proportion that is the problem. Really, that the parties are not representative and there is a lack of mechanism for a ore representative party to start and gain power. I'd argue that the same is true for Australia in that respect.
I should also point out that I mentioned a specific advantage.
I just want to point it out because I strongly advocate for cardinal systems like Approval or STAR (I also like proportionate representation). The big reason is that we have a 100+ year experiment that disprove Fair Vote's (the one pushing RCV/IRV) largest claim: "solving the spoiler effect." The math doesn't side with the claim either, but Australia is a fantastic experiment. So if we're going to do something new, why not better? Especially if better is also simpler (approval is near trivial).
