Sounds not very sustainable to me. Ruthless and speedy refactoring is only possible with tests. Better onboarding of new team members is only possible with tests. Updating external libraries is only possible with tests. How many hours did I spent in projects w/o tests figuring out what's going on... things that an easy test could have told me in the first place. In a world where cash (=time) is king, I wouldn’t mind having those dollars back.