Years ago, I tried using ghostcript to set the attributes of a webpage PDF so that it is like 8k pixels tall and had no linebreaks, but Preview.app would just render it as a single page really zoomed out, and I would have to zoom all the way in. Does it function better now?
When I open in a Preview window it behaves well and fits to the width.
Switching Preview to full screen trips it up still. For some reason that view wants to fit the whole document, and it zooms very far out to do it.
And on the iPad side there appears to be a limit on how long a document the "Full Page" screenshot will make. An HN thread with 110 comments came through entirely, but another one with 160 comments was truncated. Didn't dig any deeper than that, but I wonder what's going on there.