If you are frequently pushing to master which is deploying to prod, not having a good test stack is asking for trouble - their uptime indicates this isn't happening.
To us, the speed of deployment and overhead savings we get 24/7 is also absolutely worth those very rare issues.
Good modularization of code I think makes this more possible - the point of a big test suite is to catch unintended consequences of a change, and the less coupling the less likely this is to happen. Stuff like routers, session object and other stateful/lower level logic I'd imagine is more tricky to change without a test suite
Thanks again for the post and the candid answers!