Super! Then I definitely belong to the target group. For many years (or, even some decades), I have been working mostly with notebooks using them almost exclusively with built-in pointing devices (trackbols, Ergopoint, Trackpoint, touchpads, clickpads…). Just this experience is the reason why I would miss the arrow buttons by scrollbars.
Of course, I do not use them as the main input method for navigation within content. Arrow buttons are rather a subsidiary or fallback input method but an important one. I am regularly confronted with the situations where they are the best and sometimes even the only method to produce the needed effect. E.g., in a particular case, arrow buttons of a scrollbar can provide the finest granularity among all available input methods. Because the arrow buttons are subsidiary the small size is not an issue. But a full lack of them would be an issue.
These values are too large and they are not intended for Desktop and common situations (from the source: “Users lack the same level of fine control when using inputs such as a mouse or stylus”).
In general, we should be very careful by applying Web-standards to the Desktop. Web becomes mobile-only. There are websites where more than 90 per cent visitors use mobile devices. The button that occupies half of the screen of a smartphone can be considered user-friendly. The same by the screen of a notebook is a joke.