Failures shouldn't be judged by a standard of "this worked in my favor this time so it's good".

This time, it benefitted Democrats. Next time, with a different set of candidates, it could elect someone alt-right when most voters preferred an establishment Democrat.

And Palin definitely shouldn't have won. Most other voting systems would have elected Begich.

The problem is that IRV genuinely has a lot of weird behavior because the results are so tied to elimination order. You can actually see that visually in a kind of election visualizion called a Yee diagram, where you put candidates on a political compass and color the regions that they'd win if the center of opinion is in that region. Most systems produce sensible diagrams, IRV often produces bonkers ones.