[Smaug123]

One person's "architecture your code defensively" is another person's "make a dumb solution so that you don't waste effort being smart".

[peheje]

To me, often the "dumb" solution is the modular one, because I can't design the entire solution at once, but I can parse this string into this format, and then I can find out whether this sequence is contained in the other, and then I can map some chars to a number, and then ah..! the solution is just calling these 3 functions in the right order. Part 2 is just swapping one of the functions out with the other, great.

Now this is simplified I know, but I'm not convinced in your proposed duality.