Oh, I did see Obama as statesman-like, but thought his worldview was more "solve domestic problems, that's my sweet spot" rather than take a more central role in international politics. To be fair, he inherited the worst economy since the Depression so I get his focus of necessity needed to be internal.
I don't see Harris as vacuous, but I see her as inconsistent, which is a more nebulous word. "Slippery" is a meaner and more unfair one, and IMO doesn't apply here, especially as Newsom has cornered it. Also Harris was a tough cookie, especially as a DA in a verrrrrrry liberal place. But she can also seem devoid of ideas (a "concept of a plan"?) sometimes. Is she narrow? Maybe that's it -- maybe on issues she doesn't have a grasp of, she looks overtaxed or naive. But I also bet she's a quick study, and will take her role as America's leader (if she wins) seriously, and her gravitas will grow as it will need to.
But "Presidential", "Sincere", "Truthful" -- I agree, and Biden was all of those things IMO -- just too old.