The endurance figures for hard drives are probably derived from the rated number of seek operations for the heads, which is why it doesn't matter whether the operations are for reading or writing data. But that bakes in some assumptions about the mix of random vs sequential IO. And of course the figures are subject to de-rating when the company doesn't want the warranty to cover anything close to the real expected lifespan, especially for products further down the lineup.
For example, in the Pro-sumer space, both WD's Red Pro and Gold HDDs report[1] their endurance limit as 550TB/year total bytes "transferred* to or from the drive hard drive", regardless of drive size.
[1] See Specifications, and especially their footnote 1 at the bottom of the page: https://www.westerndigital.com/products/internal-drives/wd-r...