If everything is really true and you have been able to assess correctly, this person sounds like someone who doesn't have X years of experience but more like 1

If everything is really true and you have been able to assess correctly, this person sounds like someone who doesn't have X years of experience but more like 1 year of experience X times. Huge difference. The worst combination is someone who has been out there but still cannot be relied upon. They usually are not coachable by now. Usually. So I am afraid you can't do much here except letting them go. If you don't have authority to fire, then you need to talk to your management and have an honest conversation. After all, you are hired to fix this team.