An obvious point when you think about it, but yes you can't just assume all the Democrats that stayed home necessarily are as reliably Democratic as those that turned out. Low propensity Democrats are more mixed than high propensity.
So turnout and persuasion go hand in hand. It isn't just about base mobilization. And unfortunately Harris didn't do as well with swing voters.
Fwiw, turnout in the battleground states generally wasn't a big issue. We had a decent amount of Biden to Trump voters/new Trump voters.