My personal methodology is to alternate between iterative development and large refactors. I do very little testing during the large refactor, and test as thoroughly as possible afterwards.
If 'refactoring' did only refer to simple, mechanical changes like renaming, I could see it, but you have just argued against that interpretation.
With lots of testing, yes, you can incrementally build a working system that you don't understand. But by myopically staring at diffs all day, you'll only get farther from the truth of how your system works.
The major refactors that I do, are because I've come to the realization that my data model was not correct. A realization, that often happens multiple times during a project. My utility functions are still useful, but I have to rewire everything. There is no meaningful way to do that incrementally. Why would you even try to do that incrementally? It's like, if you have a salamander and you want to turn it into a horse incrementally. Of course, most of the RNA is the same. But testing and code reviewing the steps between salamander and horse seems to me like a waste of time.
While "if I understand the steps which got me here, than I understand where I am" may not be guaranteed (especially if you don't know where you started from), it is almost always among the more effective ways to proceed (though it is not particularly helpful if you don't know where you are going.) It can help avoid getting lost, which is one of the reasons for doing development incrementally.
There is no way in which I can see that turning a salamander into a horse has anything to do with refactoring.