>Humans are terrible at this too, but we also use more subtle and inadvertent signals like the slight movement to the line telling me they're likely about to switch lanes, only to see the signal go on halfway into it.

Isn't waymo's behavior preferred? I'd rather see turn signals well in advance of any possible lane changes, rather than the moment before the cars actually start changing lanes. Sure, it'd be ideal if the turn signals were well in advance and there were no false positives, but road conditions are changing constantly, so by necessity you're going to be trading off between advance notice and false positives.