成唯識論了義燈 5.160

5.160

答：非望自類三品而說，望總三品合斷，下三總是下品，故名究竟。不爾何故《瑜伽》、《雜集》俱但說究竟斷下品惑耶？依第二解，即無此妨。

Answer: It is not spoken of in reference to its own kind of three grades, but in reference to the aggregate abandonment of the three general grades; the lower three are collectively the inferior grade, hence it is called "ultimate." Otherwise, why would both the Yogācārabhūmi and the Abhidharmasamuccaya-vyākhyā speak only of "ultimately cutting off the inferior grade of afflictions"? If one relies on the second explanation, there is no such difficulty.