I have totally different impression: I think that whenever arrays are involved, idiomatic Julia code tries very hard to stick to the AbstractArray interface, and provides special casing (eg for Array) as optimizations when applicable.
In other words, most generic Julia methods that take Arrays will be perfectly happy with UnitRanges or whatever.
That said, I would shy away from statements like
Not because I don’t think it is true, but because it is hard to quantify or measure. Most people who like Julia have just tried it and it worked for them. (Yes, I understand that you want something for the application, but if writing it in Julia vs Python is the only selling point, I am not sure that is a strong argument).