I would agree that "unmitigated failure" is 'way too strong. US military policy was responsible for many of the shortcomings of small arms in that period of very rapid technological innovation.
One of the characteristics of the Mauser that is always cited as a great virtue for it and one of the Krag's negatives is the Mauser's higher sustained rate of fire. But the US Army was extremely apprehensive about the enhanced rate of fire of ANY repeating rifle in the hands of troops, and apparently didn't consider a higher rate of fire a virtue!
And one of the Krag's "negatives" could have been fixed by changing the shape and weight of the bullets it fired, as the British did with the Lee Enfield and the .303.
The fact that the Krag served well in the Philippines is a testament to its ruggedness and easy maintenance. Anyone who has been in the southern islands knows that they are a serious test of both man and machine, once you leave the beach.
