Wildlife and Sports photography and Mirrorless

I have a Fuji X Pro 1 and I love it.  However, there aren’t any long lenses for it yet.  I’m interested in wildlife and sports photography so this poses a problem to me (unless I manual focus with adapted lenses).  I’ve been researching a companion camera system to take care of that.  What the majority of folks have told me (even Micro 4/3 fans) is that these are two areas where DSLR’s still have a decisive advantage.

Will, what do you think about this assertion?

TIA,  Tony