I disagree; consistency is the most important part of this. With Python, you know where you stand - performance comes from elsewhere. With Julia it might be internal, a C/Fortran library, or apparently other things now too.
Did I misunderstand something?
Presumably, all fast languages are at a disadvantage, then.
This is really a minor issue stemming from the relative maturity of the languages - if Julia becomes more established I would hope usage of external libraries which don't offer a performance advantage (ie everything besides C and Fortran) eventually gets replaced with native packages to preserve the sanity of the users.
Keep in mind though, that this could be a hurdle to those who are less multilingual. So even though it's not a weakness to everyone, it is to many.