They are not. Some form of non-first-past-the-post election system is necessary for any third party to become viable. Democrats pushed for Ranked Choice Voting in Maine and Alaska. Republicans have been trying to repeal both since implementation, and now have proposed a federal ban on RCV.
It doesn't matter. Hare/Instant Runoff voting (deceivingly marketed as "ranked-choice voting" in the US) neither empirically [0] nor theoretically [1] improves the viability of third parties.
Honestly IRV is worse than plurality so there are plenty of reasons to oppose it other than a two-party domination conspiracy theory. Using IRV gives up monotonicity, possibilities for a distributed count, and some elements of a secret ballot (for even a medium-sized candidate list) for basically nothing.
Monotonicity is not a theoretical concern. Alaska almost immediately ran into a degenerate case [2].
I'm not a huge IRV fan or anything but I don't find rangevoting.org to be all that convincing from a US perspective. Most of their references and stats are two decades old or non-existent (e.g. no reference for 80-95% of AUS voters use the NES strategy). Their primary real world evidence is from Australia and Ireland, where independents and third parties currently make up 17% and 47%(!!!) of their parliaments. In the US that number is 0.3% and effectively 0% given how closely Bernie Sanders and Angus King caucus with dems.
Range voting may well be much better, and there are certainly more mathematically sound versions of ranked-choice than IRV, but I think they utterly fail to convince that IRV is just as bad as plurality. They also seem to only take their game theory as far as necessary to reflect Range Voting in the best possible light. For instance, they argue that voters will almost always rank their less preferred of the front-runners last even if they have greater opposition to other candidates, but they don't explore that candidates can and do chase higher rankings among voters that won't rank them #1. It's an obvious and common strategy (candidates were already doing it in my counties first ever RCV election) so I can only assume the reason its not mentioned is that it improves the soundness of RCV in practice.
Their link is referring to the Irish presidential election, which does use IRV—but it’s a meaningless figurehead position, so it’s unclear how relevant the comparison is.
That's a good point, I was grouping IRV and PR-STV when proportional representation isn't a guaranteed component of a ranked-choice system (though many of the dem implemented RCV systems do use it for things like county board or city council seats). Australia's House does use IRV and is at 12% (or 15% if you subtract two vacancies from the major parties).
I am a huge fan of proportional representation/multimember districts, but I think there are some valid arguments that they are not constitutional (and a lot of invalid arguments that may nonetheless carry the day—c’est la vie américaine).
other than the single-winner/multiple-winner focus problem: sure the empirics may be a bit old but there's also the theory? We don't see any reason why we'd magically get better third party support in simulations as well?
The variant of IRV that doesn't suffer this issue is to simply check for Condorcet winners at each stage. If candidate A wins every 1v1 against other candidates, don't allow them to be dropped in the runoff.
that's less of a variant of IRV than it is a Condorcet method with a weird cycle-breaking rule. you still lose monotonicity with your weird rule so idk why you'd argue for this over any of the other Condorcet methods...
though: this does go the right way. Condorcet methods are worth discussion. IRV, not so much.
Because this one can be explained to normal people who seem to like the idea of IRV and voting reform but don't want complicated elections?
IRV gets implemented a ton in the US, surprisingly. It tends to get enacted because people understand it really quickly, and it tends to get repealed because of center squeeze.
These are not the same.