Sorry, maybe I'm misreading your comment, but are you saying that julia doesn't have parameterized types? If so, that's untrue, but maybe you're saying Dylan doesn't have parameterized types? It's a little unclear in the text.

> The parameterising complicates the subtyping relationships needed to specify how multiple dispatch works.

I don't think it adds all that much complication actually, and it adds a ton of extra expressive power. For instance, our arrays are parameterized by their element type and their dimensionality, so

    Array{Int, 1}

is a 1D (vector) array of Ints whereas

    Array{Complex{Float64}, 2}

is a 2D (matrix) of Complex Float64s. This is really important for making the most of multiple dispatch imo because I can write methods which take advantage of as much type information as possible. This isn't just helpful for performance, but also helpful for just expressing your algorithm in a clear and general way.