The new battleship grey and discarding of the colourful pre-1925 liveries and evocative nameplates lent the GSR a dowdy public image, but they weren't slow to experiment with things that might be advantageous, various steam loco performance enhancing gimcracks, steam railcars, Drumm battery trains. If they only cottoned on to diesel railcars sooner, like the GWR, but the money wasn't there I'd imagine.
Steam railcars fell out of fashion quickly, but don't understand the Sentinel shunters having such short lives, they being pretty standard-ish items (apart from gauge) Presume there were plenty elderly locos which could do the same work.