Page numbers are a small additional value; pagination comes for free with print so it's an easy fallback, but there's a reason why content that is most intensely dependent on referential accessibility, like codified laws, doesn't rely on it.

> I think we need page-wise referencing on novels and prose fiction too.

It's of some use for criticism, but criticism isn't the purpose of most prose fiction. It's certainly not needed for reading, and resizability does more for the primary use than page numbering. (Of course, if you really need it, “referencde page numbering” of the type used in presentations of paginated content where page number references are commonly used like the Federal Register or court decisions when reproduced in contexts with different than source (or no) pagination can be used.)

> Reflow otherwise has always been a bane of _all_ digital books because it wasn't possible to scale content without leaving room for it.

I've seen plenty of books that aren't prose fiction that work well with reflow; PragProg epubs are particularly good that way.

> That's also the raison d'etre for other "non-web" formats, digital stores and even hardware to exist.

No, it's not; even to the extent reflow is a problem for some content, PDF had total-layout-control solved before any of the alternatives, and ePubs had strict pagination and layout control as an option since 3.0; the reason for the alternatives seem to be the same reasons for any other content toolchain, distribution, and consumption ecosystem walled-garden—it's not about serving a market need, it's about capturing a market segment and creating a cost to switch out so that you can charge monopoly rents.