My experience is that the main reason why Rust is faster than JS in some applications is that the latter tends to do a lot of copying and other memory-intensive

My experience is that the main reason why Rust is faster than JS in some applications is that the latter tends to do a lot of copying and other memory-intensive tasks - especially those related to running the JS virtual machine. If you can reduce the problem to a series of operations on pre-allocated typed arrays, JS is fast enough. Unfortunately in the case of Rollup that would be hard to do.