You could also just not vote for any other candidates if you don't think they'd do a good job. In your example, the left or the right could just not vote for the "meh" candidate if they truly don't believe they would be a good person to lead, and if they do vote for them, then they should be happy at the outcome regardless.
(That's assuming that people vote honestly, but according to at least one analysis [1], the outcome isn't very much less democratically optimal if people vote strategically in approval voting rather than honestly.)
[1] https://electionscience.org/library/tactical-voting-basics/
It may be a strategic voting: I approve anyone who is not democrat (or republican).
> The population would be better served than if one of the "strong" left or right candidates were elected.
Not necessarily. Perhaps it is better when left/right candidates alternate (driving important changes in their area of interests), than weak candidates elected every time.
Thank you for pointing to the flaws of RCV though. It has flaws, but still looks like an improvement.
In London mayor they were using "Contingent vote" system, which is AFAIU RCV with only two options, which is weaker than RCV. And in the next elections they switched it to FPTP, which is unfortunate.