Is that how it works on macOS? If so, it's plainly broken.
On Windows, and in every Linux GUI framework I can think of, clicking anywhere above or below the scroll thumb scrolls exactly one screen page up or down, for the very reason you've described. To navigate to an arbitrary spot, you're supposed to drag the thumb.
On GNU/Linux systems, at least, you middle-click to say 'go to this place'.
I love my scrollbars, and I want them always visible. I don't use the mouse often, and I certainly don't want to have to use the mouse just to see context.
Chrome implemented even worse nasties on GNU/Linux with scrollbars though, including forcing a snapback to original position if you drag the scrollbar but happen to move the mouse a few pixels too far left or right of the scrollbar [1]. Apparently that's how Microsoft Windows users do things. So now we have to as well.
Windows does it, but "too far" is actually closer to 500 pixels, not "a few". You'll certainly never run into it in normal use. I actually find it useful because I can refer to two places in the same document without losing my scroll position (I don't think that's its intended purpose, but it works).
macOS can be set to either behave the way you're describing when you click above or below the scroll thumb, or to navigate to that point in the document when you do that (e.g., click 80% of the way down the scrollbar and jump to the 80% point in the document).
On Windows, and in every Linux GUI framework I can think of, clicking anywhere above or below the scroll thumb scrolls exactly one screen page up or down, for the very reason you've described. To navigate to an arbitrary spot, you're supposed to drag the thumb.