>A ranked choice ballot at least requires you to assign a unique value to every candidate on the ballot: you can honestly rank your second choice without being concerned that doing so undermines your first.

That's highly implementation dependent. Where I live we have ranked-choice ballots for local primary elections, while the local general elections are FPTP. State and Federal elections are all FPTP for primary and general elections.

While I am free to rank up to five candidates when filling out my ballot, I am not required to use all five choices.

I can just ignore all that if I choose and just rank one candidate first and leave the rest of the ballot blank. Or I can rank multiple candidates, but I'm not required to "assign a unique value to every candidate on the ballot."

In fact, if there are more than five candidates for a particular office, I can only rank five of them.

All that said, I'm absolutely in favor of RCV and wish we had it for all elections, not just local primary elections.