The author said that Claude was not good at refactoring. But the author was using Sonnet 5. I supect Opus 5 would have done a lot better at refactoring. It would have come up with a multstep approach, i suspect.
I used Opus 4.8 to create the refactoring plans. I converted token savings using Sonnet 5 pricing at the time of writing as I'd expect to use that for more 'straightforward' feature additions.