To be honest, this seems like a bizarre choice. Rc<> would not only be more idiomatic, it seems like it would even be more ergonomic because you don't then have to worry about passing your whole Vec around everywhere you want to access one of its elements
Doing it with an indexed Vec is basically re-inventing your own memory management system on top of the native one, which as you point out can get very contrived and error-prone. Because then you also have to re-invent allocation/freeing, removal of holes, etc etc.
People sometimes do this in VMs/interpreters where they really do need custom/"unsafe"[1] memory management, which makes sense, but it's definitely not needed for application code like this
[1] Of course it's still memory-safe, but it's more fallible in terms of panics and bugs, as you've pointed out
Doing it with an indexed Vec is basically re-inventing your own memory management system on top of the native one, which as you point out can get very contrived and error-prone. Because then you also have to re-invent allocation/freeing, removal of holes, etc etc.
People sometimes do this in VMs/interpreters where they really do need custom/"unsafe"[1] memory management, which makes sense, but it's definitely not needed for application code like this
[1] Of course it's still memory-safe, but it's more fallible in terms of panics and bugs, as you've pointed out