> Even basic arithmetic operations on a TypedArray over a SharedArrayBuffer is slow AF in v8 compared to a "native" JS Array<number> for small-medium integers, because our current JIT compilers can jit the fuck out of regular arrays but struggle with TypedArray stuff. It's so sad.

Yeah, that sucks, but at least it's just an implementation problem. Java's analogous ByteBuffer methods have been fast compiler intrinsics for a long time, so there's an existence proof of this stuff done right.