You're asserting that your (or their) homegrown DNS service will have better reliability than Dyn and Route53 combined. That assertion gets even worse when it's

You're asserting that your (or their) homegrown DNS service will have better reliability than Dyn and Route53 combined. That assertion gets even worse when it's a backup because people never, ever test backups. And "ready to go" means an extremely low TTL on NS records if you need to change them (which, for a hidden backup, you will), and many resolvers ignore that when it suits them, so have fun getting back to 100% of traffic. Spoiler: I'd bet my complete net worth against your assertion and give you incredible odds. Golden rule: Fixing a DNS outage with actions that require DNS propagation = game over. You'd might as well hop in the car and start driving your content to people's homes.