I have a six year old laptop and regularly read ePubs on it (also my PocketBook e-reader) – it's fast enough. The initial page calculations can take a few secon

I have a six year old laptop and regularly read ePubs on it (also my PocketBook e-reader) – it's fast enough. The initial page calculations can take a few seconds, but this can (and is) cached and done in the background. It's not that bad and "time to something useful on screen" is more than acceptable. Large PDFs also aren't exactly fast by the way. Most e-readers are "low class hardware". ePubs work fine on most of them. In terms of performance there isn't a clear winner here; both can be somewhat slow at times for large documents, but are also "fast enough" for the common case, even on older low-spec hardware. I do think the general software ecosystem surrounding ePubs is not quite there yet, but that's mostly a matter of UX and "software that hadn't been written yet". As a format ePub is the clear winner for many (not all) scenarios. I struggle reading many PDFs because "zoom and scroll" that you mention is a right pain if you have to constantly do it (which you often do if you zoom text). Comfortably reader PDFs on my phone or e-reader is basically impossible.