As I tried to imply in my original post: Harris' talk about low inflation or fighting inflation loses on a technicality, which is that people tend to experience inflation as the current price not the rate of change in the current price. Thus, when Harris is talking about inflation fighting and inflation cooling down, you have a bunch of people who look at the price of eggs/pizza/houses and say, "this shit is still expensive, Dems are full of shit." They are not looking at the CPI, and calculating the year-over-year change.
Let me share an anecdote: I worked on a project to estimate household-level price sensitivities to the market basket of goods commonly used in CPI calculations. (My employer had shopper-card/upc/transaction-level data from tons of major grocery chains across the USA with which to attempt this project.) I tried to read through the docs on how CPI is calculated, and let me tell you: major snoozefest, and I consider myself "a numbers guy."
I doubt the run-of-the-mill American can accurately define inflation. Consequently, "look at how we fought inflation" is the wrong campaign slogan.
"The Rent is too Damn High" is still a well-recognized meme. I doubt many people remember the gentleman's name or what he was running for. But the message worked! It's got to be simple and focused.
Slogans are important. Everyone knows MAGA, it's on the hat, but can you name Harris, Biden, or Clintons?
People are suffering and the Dems ran on 'things are going great'. To the people suffering that feelz/vibez like 'our version of great DNGAF about you'. It's easy to see how that could be a less than optimal message for a candidate for election.