They are, but there has always been a contention between local admin vs domain admin (managed accounts) and usually the case has been that the domain admin over

They are, but there has always been a contention between local admin vs domain admin (managed accounts) and usually the case has been that the domain admin overrules the local but the local admin can un-join the domain. This is not that different. The moment you join the remote domain, you no longer have top privileges. You can still unjoin at any point but as soon as you join, you're placed under a different hierarchy.