Search engines prioritize the "correctness" of a document, regardless of its version, as long as a DOCTYPE is declared. It can actually be HTML 3.2, as long as it's valid (and even on this there's debate, Google for example denies). Basically, the article highlights the potential use of a validator as a linter during HTML development, regardless of the HTML being used.

The debate over the HTML standard is very interesting though; if you ever think you want to write about it, I'd gladly host it.

Thanks again for the feedback.