I think Zig being a new and a low-resource language (not enough training data) is also one of the reasons Bun decided to use Rust as large language models will simply not be as good no matter how good the model is.
Intuitively, Rust would perform worse because ownership is a different paradigm, while Zig is far more similar to things like C/C++. But I guess that's canceled out by the disparity in the language resource base.