Syntax special-cased to function parameters/arguments is more elegant than reusing the same object&spread syntax everywhere to achieve the same effect? I don't think so.

Isn't the JS version just:

    function f(x, ...args) {
        return g(x, ...args);
    }

Or did you mean forwarding object fields?

    function f(x, params) {
       return g(x, {foo: 1, ...params});
    }

JS parameters are named to some extent, as in you can refer to them by name within the function body - BUT (a critical shortcoming in my view) you can’t assign values by name when calling functions, you can only assign values by position.

AFAIK the first only works for positional (non-keyword) arguments. The second works, I guess? Not an expert in JS, especially not the "new parts", splats are definitely an improvement!

C++ has argument forwarding among its many metaprogramming tricks.