Is my scrollwheel broken? Oh, no, somebody just abused Javascript events for a horizontal scroll.
The same self-consumption can also be seen in the cryptocurrency space.
Don't mess with scroll. You will always get it wrong.
The mapping of vertical scroll to horizontal scroll is something that should be done by the browser when using a multi-column layout.
My most recent attempt is this: https://sentido-labs.com/en/library/201904240732/Xanadu%20Hy...
Right after the title there is a checkbox, checked by default, that when unchecked will lay the document out with multi-column chapters and horizontal scroll inside a chapter, vertical scroll to move between chapters.
I use a touchpad which allows horizontal scrolling so there is no need to remap v-scroll to h-scroll, but that would not work with most mice that only have a plain scroll wheel.
In practice, I too find the cursor keys (also try page-up/-down) the most comfortable way. It’s still jankier than it should but I hope that browsers’ handling of CSS scroll snap points will improve.
Although the multi-column layout works well for me, it does not for most people because of limitations in both the browser and their input devices, so I had to make single-column the default.