> there's no evidence that proportional repreesntation can achieve a higher level of voter satisfaction than good single-winner methods like score voting or approval voting
Proportional representation isn’t a method, its an axis of measurement, and there is very good evidence that better performance on that axis produces better outcomes in terms of satisfaction with government among the citizenry.
There is neither evidence nor even a theoretical reason to think that what you call “good” single winner methods (which are “good” only by abstract mathematical criteria only applicable to single-winner methods which themselves have no empirical link to good outcomes, and which make assumptions like that ballot markets have some consistent meaning across voters that are known false for the kind of rating systems they use) either would in practice perform good (or even better than FPTP) on that measure or defy the observed relation of that measure with satisfaction.
> and besides, you won't get PR at any scale beyond a handful of cities without first escaping duopoly, which requires score voting or approval voting as a prerequisite
This first part of that sentence is a ludicrous claim offered with no support. If you mean “you can't establish a better voting method without buy-in from those elected under the current methods”, that’s false in any jurisdiction with citizen initiatives (as many US states have). Whether states adopting this can be sufficient to create political pressure to negate the problem on a national basis is... well, that's certainly a question.
If you mean “no matter what voting method you adopt, it won’t produce very proportional results as long as there is an existing duopoly for incumbent officeholders in the same body”, perhaps because of some kind of partisan/media momentum effect, then there is probably a kernel of truth there, in that it will probably take more than one electoral cycle to transition to producing results close to the natural degree of proportionality of the new voting method if it is radically divergent from the former one, but that's a frictional effect, not a binary switch.
The second part, though, is even worse. There is neither evidence nor even a good theoretical argument to suggest that there is some scale where you can’t get from FPTP to something producing more proportional results without the first step being score or approval voting. And your link provides neither evidence or argument on this point, only the bare claim that the author(s) “very much doubt you are going to get it” without range (i.e., Score) voting (apparently rejecting your claim that Approval is viable) as a “preparatory step”.