Wait, really? I just can't imagine it, Umbric with and without LF is like a day and night fight. I could see the slowing effect as just Umbric ability during the fight, outside of the madness tbh.
Well, I'll believe it when I see it. Wouldn't surprise me if Blizz changed the algorithm after that one LF-free week for it to be always there after they saw how easy it was.