Humans screw up in very different ways. They don't enter intersections and then stop if the traffic signals are out.
Actually I've seen that. Yes humans do work in different ways. That's almost a bit worse than it is better. But definitely plenty of people have a freeze reaction and very much do just stop dumbfounded when something isn't working for them.
By the way Waymos don't do this either. They by default treat intersections with lights out the way you legally should: an all-way-stop. The problem is they get confused by other drivers who don't. It's a very real issue that is a problem caused by your second point: Humans fucking suck at co-ordinating. I've seen lights in in America, it's a shitshow. I've seen lights out in other countries too, in the Netherlands and Germany it's not, because the road markings determine the exact traffic order when the lights are out (which is why you see stop, giveway, and priority signs next to traffic lights).
Waymo can improve there's no doubt about it. But a large part of the problem isn't them, it's people.