Tests are only a second implementation if you use test doubles incorrectly. Test doubles should only be used for I/O outside of the program under test that you can’t really run locally / is a network dependency (eg mocking a SaaS service or something) or for performance (mocking database responses vs spinning up a test database instance). If you do it write, most of your tests are just testing each layer and everything below it.

I have yet to see a case where omitting tests actually helps you move meaningfully faster - you’re probably generating more heat than light and that makes you feel like you’re moving faster.