Max efficiency at rated power and speed was and maybe still is a big challenge.... not at rated very much in reality. The UP Big Blow was a turbine electric and didn't they make at least one run of them, like 25 or something. They were used for several years. and they did do their job as well as diesels I would expect, maybe with the exception of lifetime maintenance costs.
In reality, they would have had to build and run one to figure out the true maintenance and operating costs. That's what happened.
To say they were a failure in general because more were not ordered is maybe not accurate in the big picture. Failure suggests they or the theory did not work which was never the case.... The tipping factors were likely cost and fleet commonality that tipped the scales.
Those attempts the big railroads made at turbines were some very big dollar efforts, but as many have said, the diesel offered utter simplicity, low initial and operating cost and complete fleet commonality. Steam had no chance going against that.
I wouldn't say they were failures, rather the diesel in general offered a more (life term) cost effective and easy to work with model... pretty simple.
