Not really. It comes across as an extremely contrived example, motivated by a desire to show one language is better, and misusing the other language in order to arrive at that goal. In other words, typical tiresome language evangelism. I think your abuse of "mutable" is about on the same level of someone writing bogus code in an "unsafe" block and then complaining that his foot is gone and Rust did nothing to prevent it.

No one sane would mutate elements, free memory or throw exceptions in a sort comparison function. To demonstrate fairness, you therefore need to at least also show how you could use Rust "unsafe" to break the sort, which is also a language feature you probably wouldn't want to use in this context.