This is my setting, as well. I wouldn’t be surprised if this was the default behavior of mail clients and apps these days.
Perhaps there’s a report that indicates who has earned the welcome-related badges over time? This might possibly give a better number of who is going through the onboarding. If users are unwilling to do the 5 minute onboarding, I would 100% expect them to have trouble using a modern piece of software, regardless of what that software did. In light of that “7 users” number, I strongly suspect that “usability” is merely a symptom, and not the underlying cause.