As a Federal LEO, I would have to disagree with you.
First off, I doubt there is any Federal LEO that would risk his or her career or life by attempting to arrest a County Sheriff or any other local LEO that disputed the Feds authority.
In their jurisdiction, the locals pretty much run the show, unless the Feds want to get a court order, or have proof that the local LEO is obstructing justice and interfering with their investigation.
In most cases, both the Feds and the local LEO's know when to concede their authority or know when they have no authority. It all depends on the case and situation.
In the case that Jeff Head described, if those Federal Officers wished to continue their investigation or thought that the Sheriff was obstructing their investigation, they would have just gone and obtained a court order for the Sheriff to cease and desist. They had no authority over the Sheriff at that time and they knew it. If the investigation was worth while, they would have done just that. As it appears that they did not, then the investigation must not have been worth while in the first place.