rok, you're on a run. For my taste at least. ;^)
While I listened to a lot of folk music in high school, it was not until 20-30 years ago that I learned how much I enjoyed bluegrass/string band music. Your "Bluegrass Breakdown" sure had some hot pickin'. And the "Rhythm, Country, & Blues" was a great video introduced on PBS some time ago, after which I bought the CD. No argument with any of your choices.
Considering similarities between jazz and bluegrass, the latter does include a fair bit of improvisation. True there are favored runs or riffs that are inserted, but to my untrained ear, those are done spontaneously. In addition, compare the rhythm guitar backup with Grant Green or other jazz band accompanists. Then too, even the banjo was common in jazz groups up to WW 2. Look at Louis Armstrong's Hot Five and Hot Seven.
https://www.youtube.com/watch?v=BfORYuSJXTY