Oh yes definitely: some of the “sins” of LaTeX (doing too much with TeX macros, etc) do start with Knuth himself (though he seems to have been doing it for fun

Oh yes definitely: some of the “sins” of LaTeX (doing too much with TeX macros, etc) do start with Knuth himself (though he seems to have been doing it for fun rather than prescribing it for general use), and some are in plain TeX too. But though I wouldn't call it conflict, I think there is a difference (of focus at least), which comes across in the way they are used: Knuth does all his writing, editing, and polishing with pencil on paper, and only uses the computer to finally type it up for typesetting and fine-tuning the appearance. (Also, he tends to use not plain TeX necessarily but take ideas from it and create a separate “format” for other documents.) On the other hand, LaTeX is clearly designed with the vision of being a complete “document preparation system” for authors from the moment they first turn their thoughts into words. The former approach I guess is feasible today if you do most of your “document” stuff in another place (if not pencil and paper, then maybe a plain text editor or Markdown or…) and use TeX only at the end, for typesetting.