Saying it's "idiomatic" isn't very actionable advice for people, the average programmer hears that and doesn't really know when to use Rc over other approaches. I also wouldn't say to always go with the most ergonomic approach, that approach can lead to code that is even slower than other languages.

I would rather advise: don't reuse indices, even if that is the simplest solution that complies with the borrow checker. When one finds themselves reusing like that, that's when to turn to other more expensive approaches such as Rc.