The nerf algorithm has always prioritized lower rarity and older cards whenever possible. If they have to choose between a legendary card and a rare, they always nerf the rare. In some cases, like Scabbs this time, they have no choice but to nerf a legendary. It's an economic decision, and I can't blame them for that.
In this case, the OP is right. Knoll was fun in thief rogue and deathrattle thief rogue where thief cards were required. This dumb nerf means Knoll is only viable now with Maestra. It's a shame.