I mean we've literally done this in America (though not nationally). We've had IRV before. People turned against it. So I don't think my fear is unjustified since there's historical precedent.
Australia has IRV (has for 100 years) and is still dominated by two parties even though they have the advantage of proportionate representatives through their parliamentary system. And in reality they have their two coalitions.
What worries me is that CGP and Hasan have large audiences but look to have done surprisingly little background research into the topics and alternatives. And let's be real, voting math is hard and unintuitive. It is overly constrained and there is no global optima/easy answer. I don't expect the average person to look more than surface level, but I do expect more from groups like HN.
I am optimistic that within the last couple of years, it seems that any online conversation about RCV among even moderately technical/nerdy groups of people seems to almost always include someone bringing up the downsides of RCV and the better alternatives. I used to kind of dread RCV discussion threads because I felt like I ought to explain the problems, but it's very technical and abstract. Now I usually find someone has already written what I would have said, often in a more concise, clear way.
For instance, RCV (aka IRV) is great solution to the problem that a minor candidate siphoned a few votes away from a major candidate and swung the results of a national presidential election several times in recent memory. If voters who really wanted to vote for Nader could have also voted for Gore, maybe Bush wouldn't have won, and that election would have better reflected the will of voters.
The problem that RCV is not prepared to deal with is what happens if people actually start voting for Green or Libertarian or Democratic Socialist or whatever in large enough numbers that they actually have a chance of winning elections. At that point, you run into problems and RCV starts producing nonsensical results. The voters learn from this that it's not actually safe to vote for third party candidates, and the two party system remains in place. It's a little bit better because you don't have minor candidates swinging elections, but it's still a duopoly.