Do you have a link that explains what you're talking about? I'm having a hard time reconciling my understanding of Ranked Choice (with instant runoff) with the downfalls you describe.
Edit: I came across this: https://betterchoices.vote/Cardinal It explains the spoiler problem with Ordinal voting systems, but also illustrates problems with Cardinal voting systems. Interesting stuff.
I'm so glad I found this site! I think I've been converted to a Consensus Voting proponent instead of Instant Runoff.
You can read more about it here: https://betterchoices.vote/ConsensusVoting