That Sean Wilson video is a perfect demonstration of what I felt about thoroughbass. Seems to tell me these truths underlying the skill of an improviser remain between jazz or gospel and baroque. I think it indicates all musicians should attempt some of that even if they’re not a composer or not a performer, because it helps musicianship so much.
Reger’s book is interesting because it doesn’t teach directly what it seems to be about (practical and musical ways to actually pull off these transitions) but it does teach principles of the fastest route and common tones to get your brain moving. Particularly C to B# major. You learn these 2 chord motions and how to daisy chain them.