I haven't been using elf bane since summerset patch but I recall it used to buff Zaan proc to last 7sec instead of the normal 5. If this is still the case that means Zaan now lasts 10sec. With some weird quick maths in my head that means that Zaan last few ticks would be hitting insanely high numbers in raids.
I can't test this out myself so hoping some other peeps test this and show some results to confirm this to be true/false.