The problem with that kind of strategy is that you may be giving away the election to the Democrat.
You don't actually know, at the time that you cast your ballot, how everyone else will vote. This kind of strategic voting is difficult to reason through, and incredibly likely to backfire.
Regardless of whether anyone actually votes strategically in practice though, it seems pretty understandable that people would feel disillusioned when they see an outcome like this. Most IRV supporters say "you can honestly rank your preferences among all candidates without worrying about throwing away your vote"...and then the Republicans in that election ranked their preferences honestly, and it turns out they threw away their votes.
As you point out, it's harder to predict whether you're throwing away your vote because it's harder to reason through the effects, but I think that's just going to make even people unhappier with IRV and generate even worse election outcomes. At least in FPTP you can usually tell what the best strategy is in advance, so if you throw away your vote you only have yourself to blame.
You don't actually know, at the time that you cast your ballot, how everyone else will vote. This kind of strategic voting is difficult to reason through, and incredibly likely to backfire.