Agreed. IME the main reason to choose arena allocators is for correctness, not speed. They make similar time/space tradeoffs to garbage collectors in that they grant higher allocation throughput in exchange for more memory usage.

The perf argument against RAII is very abstract and is less "RAII causes bad performance" and more "the kind of design that leads you to reach for RAII is the kind of design that's bad for performance." There exist similar hand-wavy arguments against many other C++/Rust features.

More generally, "you shouldn't even want that" is basically a meme at this point in programming language design. Every new-ish language has some version of it.