Dopesheet mousewheel scrolling shouldn't be slow. What OS are you using? Are there settings for your mouse to scroll X lines at a time? How does scrolling in a browser compare to in the dopesheet? We could provide a mouse wheel sensitivity setting, though first we'd want to be able to replicate your "too slow" scrolling.
Left click drag is used for selection. Right click drag does scroll, but only horizontally. I tried it vertically and it's a bit odd. What works well in the viewport is a specially crafted scroll/zoom combination, but in the dopesheet we don't have that type of zoom. Panning 1:1 mouse pixel movements to dopesheet scrolling is slower than using the mouse wheel. Multiplying the panning by something like 5 is a little more interesting, but mouse wheel scroll still feels more natural IMO.
Are you using the dopesheet lock and filters to reduce the number of items shown?
Dopesheet - Spine User Guide: Contents
