Disagree on several levels. React gives a _much_ more powerful mental model for how data flows through your system, especially when used with Redux. Debugging a React app generally involves just tracing data flow backwards through the appropriate components or Redux actions. With Backbone, it could involve arbitrary event chains and model mutations invoked anywhere in the codebase.
With Backbone, I liked that the core library was simple enough and everything was synchronous, so I could step through Backbone’s code and back out into my own to trace what was going on. With React, yes, an error usually results in a long stack trace of React internals… but the error message is almost always enough to tell me where the symptom is and what’s going on, and that’s enough info to trace things backwards, so I don’t _need_ to go through React’s internals.