The MLB on-call blowout pitcher should be like the NHL dentist; a local guy who is on duty at the stadium for the duration of the game, prepared to serve *either* team when things get bad.
This way there’s no extra body to take on road trips, just a roster of local men’s league pitchers in every MLB city that are on call. They don’t know if they’ll be pitching for the home team or the visitors until the time comes, but either way they have every reason to try to bring their best stuff and make competitive pitches — it might be the only time in their life they get a look on a big league mound.
It would be so much more fun to watch a 53-year-old Everyman pumping 82 mph but still trying to go after hitters while wearing a #89 jersey with no name on the back than random position players throwing literally HALF that hard and not caring.