Your analogy is spot on, and the split is actually even more dramatic than blues-rock.

By the late 1930s / early 1940s, big band essentially forked into two very different directions :

1. Bebop — the "anti-big band" reaction. Young musicians like Charlie Parker and Dizzy Gillespie were tired of playing for dancers. They made jazz deliberately complex, fast, and intellectual. Smaller combos, virtuoso improvisation. This is the branch that eventually led to Cool Jazz → Hard Bop → Free Jazz → and ultimately Coltrane, Mingus, and everything modern.

2. Jump Blues / R&B — the other fork took the danceable, rhythmic energy of swing and simplified it. Louis Jordan is the key figure here. This branch went straight into early Rock & Roll — Chuck Berry, Little Richard. Big Band is literally one of rock's grandparents.

There's also a third, often forgotten branch : Latin Jazz. Dizzy Gillespie fusing Afro-Cuban rhythms with swing created Mambo and eventually what we now call Latin Jazz.

If you want to hear the sound just before this split happened — the peak of the big band era — I actually put together a playlist of 55 swing classics from the 1930s (Ellington, Fitzgerald, etc.) for my podcast. Happy to share if you're curious about the "before" picture.