Perhaps another consideration would be whether or not de la Maza was even qualified to take readers past a 2000 rating. ("He ... retired from active play with a 2041 rating." - IM Jeremy Silman (~2002)) I think that IM Smith (with his chapters on positional chess, openings, endgames, etc.) was trying to offer material that could be helpful for the reader hoping to get well past a 2000 rating.
400 points in 400 days
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Yeah, the drills are mentioned in his articles too, I think. It's been a while. Still, the breadth and quality of the material in the Smith book seems a lot better going by the reviews.