Doing so would require the app to have the business logic written in JavaScript. Apple only allows JIT’ing JavaScript using JSC.

This seems to be a weaker claim than "RN is needed to do this", but practically speaking it might amount to that.

Sure you can choose not to adopt React’s reactive paradigm and manage state directly but using JavaScript. My understanding was that in RN, JavaScript code manipulates C++ objects in the C++ part of RN, which then calls host platform code to create views and render.