Does self-serve onboarding actually work for products with a learning curve?

We deliberately avoided adding forced product tours or initial setup calls because we wanted a totally seamless, self-serve sign-up flow. But tracking analytics showed that users who didn't complete setup within their first 15 minutes almost never came back. Adding just one required setup screen cut our drop off rate significantly.

Do you prefer keeping onboarding completely frictionless, or is adding a bit of friction worth it if it guides users to value faster?