I think the claim here that: “The "radical" US left equals the conservative right in many European countries” is a bit of an exaggeration. A more accurate statement (and probably what OP meant; albeit less inflammatory) would be something like: “Moderate and conservative (i.e. mainstream) Democrats in America closely resemble the conservative right wing parties in Europe”. And I think this is largely true. Biden is in many ways to the right of Macron even though Macron is in the center-right of the political spectrum. While Bernie Sanders (the most left wing the US could possibly hope for) really only approaches the center-left Olaf Scholz.