I believe the point is that if you're unhappy with the default scrollbar, you should get rid of it altogether rather than torture it into doing something it's not meant to do.
Having done e.g. an endless scroll application, the scrollbar was unfit for our use, no matter what we did. The right solution was to remove scrollbar and implement our own scrolling mechanism.
Which is straight up what jmbwell was complaining about, as it breaks their workflow such as tapping on the top to scroll to the beginning and everything else they mentioned.
There is no beginning in the thing I was talking about. Which is why removing the scrollbar and breaking people's expectations in a way they can see/understand was better than trying to repurpose the scrollbar.
It breaks more often than it doesn’t. Yes, the page “scrolls”, but it scrolls only a few pixels, while the internal “custom” scrolling implementation doesn’t respond to the event and does not scroll to top, resulting in a terrible UX.
When you scroll on reddit, there is a beginning and no end.
Some applications have neither a beginning nor an end, so scrolling to the beginning makes no sense. At best, you could make "scroll to the beginning" get back to the start of your navigation, but then your scrollbar wouldn't let you go further.
(also if you have both horizontal and vertical scrolling, you're still left with no horizontal options)
The GP was specifically complaining about apps not respecting their scrollbar choices. They said that apps should defer all scrolling UX to the OS, as that is what the user chose.
Having done e.g. an endless scroll application, the scrollbar was unfit for our use, no matter what we did. The right solution was to remove scrollbar and implement our own scrolling mechanism.