For example this: https://www.cgtrader.com/3d-models/military/armor/10-warrior-helmets
It's not high quality. Low-mid quality (and that's in the best case).
Example high quality helmets: https://www.armorhead.store/helmets/
Even without wireframes it is already clear that there is nothing in common with the “clean and principled topology”.
It's the same with all other models and brushes. All done very fast and very carelessly.
Regarding descriptions. If text was compiled by a copywriter who, in addition to this, within an hour wrote twenty more articles on various topics (none of which he understands anything about) then of course there are no any questions, ok.
Cutting of the stones on 7th render called “Too much schnapps” or “Heating turned off”?
Learn in more detail about retopology, Lazy Mouse and EdgeLoop settings and more practice with them.