Most passengers don't care, only the foamers.
480 apparently handled the train solo except on the ruling grade, so it was steam only for part of the trip.
From a practical sense, adding or removing a helper from the point is far easier than cutting it into the train (other than the rear) or behind the lead engine. During the transition era it was common practice on many railroads to keep diesel ahead of steam allegedly to limit the likelihood of the diesel engine and air filters from having to deal with investing any steam loco smoke.
Depending on the load from the grade, train and curves, it's better slack control to have a steady pulling diesel in the lead versus a steam loco slipping out. The Loop found this out the hard way when the crew decided to run the 12 ahead of the 21 years ago.