I once made the mistake of saying that the demise of the steamer was because the diesel was more powerful. The general manager at the Angus (CP) yards in Montreal gave me a good talking to telling me the only reason for the diesel was because it got rid of several employees i.e. the fireman as well as the need for water towers and coal bins for "refuelling" and the manpower attached to that. He said the steamer could out pull a diesel any day. Don't know about the current generation of diesel's though. Now-a-days it is possible to stagger the locomotives within a train so that you have some pullers and further back a puller/pusher unit.How much torque did those monsters have and how did they compare to the modern diesel/electric?
You can imagine the manpower to run several steamers together with the firemen etc. Plus the electronic controls to enable everything to work together with the diesel units is probably a lot simpler.