I have been playing runic corruption with festerblight and it seems to pull ahead of blood tap when it try it out but i can't figure out why most dks are blood tap specced since runic corruption makes diseases stacking with festering strike alot faster.
Is this due to the execute phase that one can always soul reaper with banked charges or due to blood tap not RNG?
Was looking over this the other day, if you look through the top 20 - 30 odd UH Death Knights the vast majority of them are actually using Runic Corruption.
I just think its because festerblight is relatively "new" and people are still working out how to play it the best, that things like using Runic Corruption over Blood tap hasn't trickled down to the majority of players.