It is LLM with a clever prompt that avoids the most egregious tells (though "load-bearing" appears).

The number of times the article goes on complete tangents, introducing new irrelevant names and the general useless level of detail, all in perfect verbose English points to an LLM. So does the upbeat and persuasive style.

If you write that level of detail, use a historian's style and footnotes. Do not use the synthetic LLM voice that is optimized for rhetoric.