FPTP might be the worst, but IRV is a close second. Just like FPTP it gives significant artificial advantage to a certain kind of party. Specifically, IRV tends to elect a party that is most people's second-choice party.
You might think that's good because such a party will have to be more centrist than what FPTP is likely to elect, but centrist doesn't necessarily mean good. If there is no competitive pressure for a party to be good, it will not be good, centrist or not. It will be centrist but will become just as corrupt as the parties we have today, if not more.
That's because this centrist party will not actually face the higher level of political competition you'd expect from a non-FPTP system. It will get second-choice votes it needs for a win very reliably, because both right wing and left wing voters would rather take this centrist party they don't like than allow the other wing that they hate to win.
So with IRV you can easily end up with the same centrist party winning the election over and over and over again.
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Since we just had elections in Canada, fun fact: the last time around our future prime minister, leader of a centrist party, promised an election reform if elected. After his party was elected, he revealed that he only wanted IRV, and would not have anything else. Now you know why.
yes, but maybe we shouldn’t let perfect or better be the enemy of what is actually needed (to paraphrase alan kay)
iow, what are the actual problems we are trying to solve, and what is the election system that is actually needed to solve it
the potential problem of choosing something “a little better” is that we could get stuck in another local minima, where further reform (that is needed) doesn’t happen because the new current system is “good enough”
FPP is widely acknowledged to be the single worst way of holding an election.