> It is not known whether proportional representation can compete with the best single winner voting methods.

I don't know the metric you are using here, but it is surely purely academic, as the rest of your comment. The idea that a single candidate can better represent a smaller (and usually gerrymandered) district than a larger number of diverse candidates in a larger district flies in the face of everything we know about real democracies and party systems.

> Your scenario is unrealistic because real humans aren't that tightly clustered, so you get defectors.

Again, theoretical claims against real world experience. I've experienced polarization in AV to the point where center becomes a wasted vote, and people are incentivized to support one of the two dominant slates.