> 4. Any sort of refactoring that may adjust ownership. E.g. going from T to Rc<T>. GC requires fewer choices so these refactorings are easier.

This pain is real. I've been using Rust for four years now, and it hasn't gotten any easier. And unfortunately, the best strategy I have for refactoring is still "start refactoring; then see what issues come up and if I have to revert".