The Australian iron ore roads rated their 16-251's at 3000 hp-and I believe Cartier derated theirs as well. Some of these engines had even been upgraded to the so-called 'heavywall' block.
That said, the 251Plus variant addressed various durability issues with P/A's, cams and other areas.
Suppose that the virtue of a cast block is that the designer can more easily put more metal where the stress concentrations are. In the case of DLW, they have been bumping up their production year after year-and one of the ways to do that is to outsource component manaufacture.
BTW, the same outfit has been able to uprate the EMD 16-710G3 from 4000 to 4500 hp !!
Stupidity is the basic building block of the universe.