https://pages.oils.pub/spec-compat/2025-06-19/renamed-tmp/sp...
(which I created)
Even the upcoming bash 5.4 implement ksh command sub ${ echo hi; }, which is more evidence that bash is based on ksh.
They're still implementing ksh 35 years later ...
"Foundation staff member Brian Fox is now implementing an imitation of the Bourne shell."
https://www.oilshell.org/archive/ksh-usenix.pdf
bash implemented essentially all Bourne shell features a long time ago -- and for the last decade+, and currently, it's implementing ksh features
I'm not sure why it's hard to hold those 2 ideas in your head at the same time
