As referenced in sibling comment, I took 121 a bit earlier than that, with Prof. Lewis. Of course he taught from his "Turing's Face" textbook, which is widely touted as accessible to students with high school math. By the time I took 121 I had quite a bit more math than that so I can't recall whether that is true. I agree with your "tedious and fiddly" assessment, but I don't see any way around it. CS is a tedious and fiddly subject anyway, but the fiddly tedium in this case is related to foundational truths about computation rather than trivial details of particular algorithms (...or, at less ambitious schools, APIs). Frankly, I hope it's never the case that a student could graduate Harvard with a degree in CS (or applied math) without mastering the material that Prof. Lewis taught in CS-121.