Butchering efficiency REDUCES the amount of meat you get
Without Butchering Efficiency, I can get 10 meat from 1 Elk. The Butchering Efficiency is stating that it decreases the cost of making Raw Meat, etc. So I would assume that to say, when I order 100 orders of Butcher Elk, I would only need, say, 89 Elk and get 1000 Raw Meat. The Elk cost is correct, BUT I only get 881 Raw Meat. This means I'm getting less than 10 meat / Elk :/.
Coincidentally, I would change how the Efficiency skills work for "1 item turns into 10+ items" - instead of lowering the input cost, it would be great if it increased the output. So say, 10% butchering efficiency would mean getting 11 meat from 1 elk, rather than taking 9 elk to make 100 meat.
Great man, very good point