Route 53 also has no IPv6 support, and no stated policy on how it deals with DDoS attacks, or if you get charged for the attack if it's directed at you. Good luck!
For DDoS attacks, I'm not sure what you mean by a "stated policy." They do a lot of countermeasures, some of which can be found via linked PDFs at https://aws.amazon.com/security/ Various R53 items are included in their DDoS document there. Officially you get charged. Unofficially, it depends on the circumstances. There's also a world of difference between a DDoS attack against a fully managed offering (like R53) versus, say, an EC2 instance.
Have you seen a better approach taken by other providers? I don't mean technical approach (which is near impossible to compare other than by track record), but from a policy perspective?