Indices are the way to go for a whole range of programs - compilers (IR instructions), GUI (widgets), web browser (UI elements), databases, games (ECS), simulations, etc. It is however without borrowcheck guarantees.

Rc and Arc are definitely a bad way to avoid borrowchecker. GC is used because it is much faster than reference counting. OCaml and Go are experimenting with smarter local variable handling without GC. At that point they may outperform Arc and Rc heavy Rust code.