Many of the standard unix tools are not written in sh. They're written in C. Am I missing something in your comment?
I think the point here is that DOS explicitly rejects the composition that pipes enable, in exchange for the ability to just hand "the whole system" over to a programmer.
But the main point, that DOS was basically a thin program loader that "got out of the way" is sound. Think of it like a UEFI shell environment, with 640k+ limits.