Even then, a new user account doesn't necessarily mean a new user.

Every time I start on a new job, I have to click through Slack's, Github's and many other dev tools' stupid guided tours for the hundredth time

If your usability is good, you don't need a guided tour even as a new user because you can just figure out as a new user how it's supposed to work and get your job done. Guided tours and documentation should be limited to expert features that only a very rare subset of people need. The things everyone does should be obviously easy to use right away and so no helping or tour is needed.