For that evidence they’d need to look to Congressional downballot races which are more fluid and open to experimentation. The evidence of progressive voter mobilization doesn’t show up there either.
Funny enough, the two Florida democrats who lost in blue districts also specifically distanced themselves from a ballot measure to raise the minimum wage on the basis that it was too progressive - both they and Biden lost in Florida while the ballot measure passed.
Progressive policies are broadly popular. Running on things that are popular tend to get you more votes. People like it when you do stuff for them.
The only evidence I've seen to the contrary is a NYT opinion piece that cites centrist think tanks and random people's opinions. I didn't see anything in there that looked reliable or compelling.