I've heard that Waymo relies on having very accurate map data for the areas where they operate, so perhaps they could perform worse than human drivers in areas where they don't have good map data.

But I also trust that the company wouldn't deploy them in those areas until the quality data they need is available. So perhaps "safer in the environments where they are actually deployed" would be more accurate, but that's also the only thing that matters.

Speculating about what would happen if they were used in ways they are neither intended to be used nor are actually used feels a little silly. Most machines can be unsafe if you use them in ways they're not intended to be used.