That is incorrect. Legally under the Air Carrier Access Act, ESAs are protected as well as service animals. Service dogs do not need to have specific paperwork. Now, most airlines do require you submit specific paperwork for ESAs and psychiatric service animals. Some have limited ESAs to flights less than 8 hours. They cannot decide "actually, we don't want this ESA on the plane" willy nilly though. They can still dismiss an animal for behavior or if they cannot fit at your feet without impinging on other pasengers/asle spaceAs you know, ESA's do NOT have access while Service Dogs do. ESA's are not service animals. As you note.. Butters is a pet.
Some airlines allow ESA's to ride in the cabin. Others do not. Many are going to NOT allowing ESA's to fly in the cabin. They are not trained service animals and do not have access.
More concerning than the flight time, for me, would be the extensive quarantine procedure animals coming from the mainland must go through to enter Hawaii. Service animals can be pushed through with very specific paperwork, but ESAs are not included in this, and it is a tough process even for service animals.