Julia has been designed for single core performance fullstop. Functional collections may work well with a state of the art GC, with Julia's not so much. The fact that Julia can interop seemlessly with C code (easily) kind of bounds the design of the GC.

I think it is a little disingenuous to say that a Julia programmer does not have to worry about types. Type inference alleviates many burdens, but correct typing of arguments is essential (and hidden promotions or casting can kill performance). So while you can write correct programs easily, for efficient programs you end up worrying about this quite a lot.