That was true for Obama, as well. But the 50 state strategy was still a good idea, because states aren’t monolithic. If you try to win over Utah, for instance, well, you’re not going to succeed in winning over Utah. But that effort might also swing a few LDS voters in Nevada or New Mexico, and that could make a difference. And there are some states that are unlikely but not impossible pickups, like North Carolina or Ohio, and also states like Texas, which the Republicans aren’t going to lose if they put any effort into defending them, but you can force them to put in the effort.
With a whole two election cycles of precedent, but yes. If Obama endorsed someone other than Harris, that would be a big deal. But him just staying out of it (until it’s official) doesn’t really hurt her.