After Walter Mondale in 1984, were the other democratic nominees considered centrists? Michael Dukakis, Bill Clinton, Al Gore, John Kery, Barack Obama, Hillary Clinton, Joe Biden?
In the primaries from 1988 to 2020, there were more left-wing candidates: Jesse Jackson, Tom Harkin, Bill Bradley, Howard Dean, John Edwards, Bernie Sanders.
In 2004, it was a Republican talking point that John Kerry was the most liberal sitting senator.
In 2008, it was a Republican talking point that Barack Obama was the most liberal sitting senator.
Heck, even in 1992, Bill Clinton was attacked as a dangerous "McGovernite".
It's only in retrospect that they seem milquetoast.
The common denominator here is “Republican talking point.” Of course Republicans will claim that the Democratic nominee is more liberal than they actually are.