The 66-page "Breaking Paragraphs into Lines" is a research paper, and much of it is is the "complexity" of the problem itself, rather than TeX's elegant solution in particular (e.g. pages 48–59 are about history). In a sense, the generality shown in the paper (the various different things that TeX's algorithm can accomplish) shows how TeX reduces the real-world complexity of typesetting with a simple approach that covers all of them.

The book "Digital Typography" is, somewhat misleadingly, not a book that was written about digital typography, but simply a collection (https://cs.stanford.edu/~knuth/selected.html) of several papers that Knuth wrote about TeX and Metafont and some related topics, over several decades.

Maybe the several hundred pages of the "Computers and Typesetting" series would be a better example for your point: https://cs.stanford.edu/~knuth/abcde.html

In any case, I agree with the comment you're replying to: if you use TeX itself without dragging behind you the entire ecosystem and all the packages (in particular, use plain TeX rather than LaTeX) you'll see it's not really complex, and the implementation is fine. Especially today, with things like LuaTeX scripting (and, say, opTeX) it is feasible to bypass LaTeX and packages and do things yourself — that is, unless external circumstances require you to use LaTeX and packages etc, which is still often the case (e.g. submitting papers to journals).