Code review is really just one part of a Witness job, and certainly not the whole thing. You make it seem like the whole thing.

In your scheme (the post image) witnesses don't get to propose code? Is that not our function? What about design scope of new code to add? Should we have input into that?

Reviewing the code that you plan on running should be your most important task beside running said code at scale.

I consider code review and testing to be technically as hard if not harder than writing it.