It is realistic as locomotives are coupled together will all sorts of locomotives! It’s for the super heavy long haul freight trains that may have a road only locomotive consist as these trains move cross country and all that extra horsepower is necessary for hill climbs and keeping the train moving. But sometimes those locos aren’t available so the railroads have to rely on switchers and older models to haul trains, which may result in more locomotives in that train. Even this is possible!