Actually, proportional representation would likely give more to centrists who would always hold power as the median vote in a PR system.
In a FPTP vote system, Bernie can win a 35-40% of delegates, become the nominee, win the general election, then have a Cabinet of like minded folks and be able to completely shift the Overton Window by appointing people to various offices, just like Reagan did in '80.
OTOH, in a PR system, even if the Social Democrats won the most seats, they'd still be in a coalition with moderates who'd hold key seats. How is Bernie going to push against Wall Street corruption via the DOJ or various other orgs if the moderates say, 'put our people in those cabinet positions or we ally with the Libertarians and form a government.'
Ironically, PR was first pushed by liberal parties in Europe worried the socialists would overwhelm them in a FPTP system. -
https://twitter.com/davidshor/status/849651876735967233 /
http://web.stanford.edu/~jrodden/Manuscript/shadow.pdf
Now, I still support PR, but also don't think it'll be a boon to the Left that they think it'll be.
Also, a reminder - most Democrats disagree with liberal orthodoxy on at least one major issue -
https://twitter.com/davidshor/status/855478654264123393 /
https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/HOH1F0
Also, the American electorate in general, is right wing compared to the rest of the world -
https://twitter.com/davidshor/status/942627284174934016
Europe passed social welfare policies, even with PR giving more power to the center because it didn't have wacked out racial policies. Now, we're seeing in real time, what happens to European policies when there's an Other to go after and hey, the same thing that happened in America is happening there.