It's very important to play around and experience a feature in the wild for iterative process. Once you've designed onboarding which includes getting started tooltips and emails, it's difficult to experience it as a new user. How do designers experience onboarding themselves? Do they create a bunch of email ids and sign up and then wait to see what emails and tooltips they see? That sounds very cumbersome.
yes, it's a biased experience for the creator of the feature as they are not only familiar with it but it matches their mental model of the product. user testing on onboarding must be done on users who weren't involved in the creation of the product or it's features. also its better that these users are not in the industry of ui design or tech.
As a Designer, we are designing for an intended user experience, and because of this, we can never experience this like a real user who encounters it for the first time.
You really need to perform usability testing with real users to capture how they feel about the solution.