So... Oppression?

You never really hear about the usefulness of this mastery in the first place, but then they move it up the page and take off a percentage? What?

It's usefulness is difficult to perceive because only specific champions make real use of it. Reason being that hard CC makes enemies stop dealing damage anyways, and expecting to reduce delayed damage is assuming too much against anyone that doesn't use DoTs.

Maokai, Gangplank, Nasus, and maybe a handful of champions that could exploit Rylai's (namely Amumu and Sej), are the only ones I can see using it to its full potential, so did they nerf it just to keep them in check or something? Moving it up in tier only to decrease its value seems like a mistake.