Take every non-trivial side project you ever worked on and calculate the percentage you completed. Not half ass completed, but actually completed completed. Like you commented everything, wrote documentation, put it on Github, have decent test coverage, etc. Or how many Coursera courses did you sign up (with the real intent of actually finishing) vs how many did you _actually_ finish, doing all the homework, getting a really good grade? Employers look for people with degrees because it's very good estimate for "this person can finish shit" for this very reason.
To say PhD is "just a credential" and has no predictive capabilities in terms of being "successful" I think is being disingenuous.