I'm not disputing that. In theory Rust should outperform even today but of course reality is a different beast and implementation details are important.

Then you also get into architecture specifics etc.

dodobirdlord described the two major advantages Rust has on the language level very well so I won't repeat them, but the gist I'm making is that Rust simply allows more optimizations purely on the language level. Specifics of backend implementations are of course another topic completely (and is one of the reasons why I'm excited for the possibility of a GNU Rustc)