@sdunham The Netlify system for removing a domain from an account to allow its use within another account is manual on their behalf and subsequently frequently causes drama.
As non-enterprise accounts are considered to be ‘self-service’, I requested that it be made self-service three years ago, but there’s been no movement on it.
It’s obviously worse in your case considering that you asked in advance in an attempt to avoid it.
I suspect the statement in your original post of “It’s set up as a new Netlify site on the same account as the existing site.” would have caused everyone, and the AI included, to presume you wouldn’t encounter the issue.