This isn't a function of how difficult it is for the pirates themselves to get their hands on a DRM-free electronic copy of a book. Instead, it's primarily a function of the fact that piracy is illegal, and—regardless of how easy it is for pirates to obtain DRM-free copies of the media they want to distribute—such distribution activities are limited to dark and relatively lawless corners of the internet where "normies" fear to tread.

That's the basis of my point in reply to you. It may be that DRM prevents to some degree the more casual form of "piracy" in which e.g. I give a friend a copy of an ebook file instead of lending a physical copy, but that didn't seem to be what you were getting at, and anyway since lending physical copies has been a possibility since books first came to exist I think the degree to which this sort of casual piracy threatens publishers' bottom lines is not a foregone conclusion until some independent party convincingly measures it.

> if this solution isn’t working, or looks unfair, how are we going to solve it differently?

OP's article makes some recommendations under "Conclusions".

In terms of how DRM is cost-effective for platforms and publishers (i.e. why they bother with it at all), it seems much more likely to me that it's primarily meant to prevent fully legitimate post-first-sale transfers of books, e.g. library lending, second-hand sales, and so on. Publishers couldn't do anything to stop post-first-sale transfer of physical copies, but DRM-enabled ebook platforms give them a new lever.