Amtrak used to have an Onboard Service Supervisor until about 2001/2002. Then, from what I have heard, the "Union" members did not like to be managed on board by a management person and they wanted a Union person. An argument ensued, which finally led to removal of the Onboard Supervisor, and everyone, except the poor Customer was happy I suppose. That is where it stands at present. Apparently someone has to come up with a way of doing it that is acceptable to the relevant Unions on this one and most appear to feel their time is better spent elsewhere. As usual, the Customer suffers.
If you are referring to the position titled: “Chief - On Board Services”, which indeed supervised on board service personnel on long distance trains, but was subordinate to the Conductor and Assistant Conductors; that was a so-called “partially exempted” union position, represented by the ARASA—American Railway and Airway Supervisors Association,division of TCU, now part of IAM.
The “Chief” rode trains such as the CZ the entire way with the crew, and reported to that train’s “Train Manager”, at the home crew base of the train…in this case, Chicago. The Train Manager, which was a full management position, spent about half the time at the base, and the other half on the train, or maybe turn around halfway, to monitor the Chief’s performance.
“ Partially exempted”, in contract terms, meant management could selectively fill the position based on merit, without regard to seniority. Chief’s were usually chosen from the best train or service attendants by management.