Thats not a unique change to snowdrift, so it wasnt actually a targeted nerf.
thats a change that happened to all effect items, and passives! Ailment effect got deleted and replaced by Pen as an entire ailment system rework.
And yes, its bad and nerfs most ailments by a minimum of like 15-20%
Ailment Rework a Failure? - #8 by Metal_Bawkses more reading on a recent thread talking about it.
Tldr; DoT still strong, but most ailments doodoo.