IRV isn't perfect, but it's a huge improvement over the current state of affairs.

I would point out that the "won't elect a centrist" perspective might be a bit of an American perspective and a perspective that might change with IRV.

For example, let's look at Canada. You have approximately from right to left, Conservative, Liberal, NDP, and Green. There are districts where the Conservative party won with around 30-40% of the vote while left-of-center parties gained 60%+. I'm guessing that most people that voted Green would prefer a Liberal candidate to a Conservative one. Similar for NDP voters. In that case, votes would have been transferred toward a more centrist party.

I think in the US there's also the trap of the primary system. Primaries often have extremely low turnout compared to the electorate and so finding an energetic base can swing a primary in a way that it can't swing a general election. Many people who are more centrist don't vote in primaries.

Frankly, you might just be underestimating how many centrist voters there are in general elections compared to primaries. Even as the Democrats have lots of great candidates, Biden is still topping the polls so far.

IRV certainly isn't perfect, but it's an incredible improvement, easy to explain, easy to trust, etc. It might not end up with the candidate that is the most acceptable by some weighting system, but it does favor people with broad appeal.

Honestly, if we got rid of the primary process and had a hypothetical general election that was Trump, Romney, Biden, and Warren, I think it's very likely that Romney or Biden would win. I think the big issue drawing parties away from the center is partly that primaries are decided by the small number of people who show up to them. If there was one general election with many candidates, it would likely be a different story.

Heck, if the Republican primaries had been IRV, Trump likely wouldn't have been the candidate. Even if he was popular on the extreme, more centrist votes would have coalesced around someone else.

IRV is simple and trustworthy. Borda, frankly, seems difficult to explain and trust. Ok, let's say that I have 4 Democrats and 1 far-right Republican with a uniform distribution of the 50% of democratic votes for the democrats. With 10,000 voters, the Republican gets 5,000 points. Each Democrat gets 1,250 * 1 + 1,250 * 0.8 + 1,250 * 0.6 + 1,250 * 0.4 which is only 3,500 points. The Republican wins a landslide victory despite an evenly split electorate. Or do you force people to list all candidates?

Heck, let's go with Bush, Gore, and Nader. Let's say Bush gets 48%, Gore gets 37%, and Nader gets 15% (and assume that Nader voters aren't going to vote Bush). With IRV, it's easy. 13% protest-vote for Nader and Gore gets elected once their votes transfer. With Borda, it's more complicated. Bush gets 48% of the points and then Gore gets .37 * 1 + .15 * .67 which is only 47% of the points. Bush wins - but that's not what the public wanted to happen. They thought they could vote for Nader first without hurting Gore!

IRV does have tactical voting considerations, but they seem really simple to understand and trust by comparison.

IRV isn't perfect, but replacing a voting system requires something that people easily understand and trust. People easily understand the implications of ranking and eliminating the bottom person, redistributing those votes. They understand how it eliminates spoilers and lets them vote for who they want in the order they want. A points based system is a lot harder for people to understand and trust. Again, IRV isn't perfect, but if we're going to have change, it has to be easy for people to understand and accept. Personally, I prefer single-transferrable-vote and multi-seat constituencies, but that requires radical change to our system. IRV is a simple change that people intuitively understand, accept, and that so many people have wanted for decades now.