Biden was the most centrist of the Democratic candidates, and is considered center right by many. It's hard to argue that presidential elections have become more partisan and polarized.
That’s not even getting into that the claim of Biden as “center right” is based on Overton window shifting. Biden repudiated many of his earlier more centrist positions on DEI (e.g. his anti-school busing activism in the 70s), immigration, abortion, etc to win the nomination. Compare Biden’s platform and positions to the Obama 2008 campaign platform and can you really see it as a “rightward” shift?
[0] edit - see for instance https://www.pewresearch.org/short-reads/2024/03/19/about-1-i...