>>1769985>Steam turbines generally operate most efficiently at one rpm range, and suffer heavily at other rates.You are correct in this, but a locomotive with turbines designed to be a max rpm around 30mph will easily climb hills with no issue. The Swedish railways did this with some old 0-8-0s that hauled iron ore. Replaced the cylinders with a turbine and added a pony truck to carry the extra weight.
Link with a bit more info from 6the paragraph onwards:
>https://wondersofworldengineering.com/turbine-locomotive.htmlYour point about the big 3 is interesting, I guess they got too complacent with steady sales. Until diesels came along and the had to scramble to meet already established competition from EMD.