I think it's more accurate to say that you don't believe it is shaft speed. Your belief is incorrect. Mike Page has a video on YouTube that explains why beginners are unlikely to get the same maximum spin as Mike Massey. I think it's under the FargoBilliards channel: https://www.youtube.com/results?search_query=fargobilliardsYes, but my overall question is what makes "the stroke" for these gifted few? I don't think it's speed of the cue shaft, however. ...
If you want some more technical details, look at Dr. Dave's website. One surprising thing there is that for some draw shots you don't want to hit as far below center as possible to get maximum draw distance on the cue ball.