We can make an informed judgement because we’ve seen the Democratic Party refuse to to change throughout the last ten years of Trump candidacy and election… not to mention the issue that likely cost them the election to begin with.
Biden quitting was a big change. Not enough to win the 2024 election for Harris, but still a change. I think failure is the biggest motivation for change, and the Dems have failed bigly. I think there's a decent sized chance they run a more populist candidate in 2028 and maybe the mid-terms too.