I think this post helps to explain two phenomena about Direct Instruction: first, why it never expanded into secondary-level content, and second, why so many teachers feel instinctually averse to the DI approach. At higher levels (and in content-rich classes like history and science, where DI has never done much at all), the questions about what to teach and the connections between ideas are much more important, which makes DI programs much harder to write. DI has often been accused of being rote learning. The Project Follow Through evidence contradicts this, but we should remember Project Follow Through was only done in grades K-3. You can get great results on problem-solving measures in those grades just be being the best at teaching kids to read! Qualms about rote learning point to a real problem that you are highlighting. DI managed to sidestep much of that by focusing on the places where, as you say, decomposition is the most straightforward.

Great food for thought, thank you for writing!