IIRC, when the type advantage multiplier was 1.4x Fury Cutter was better against a target with a single grass weakness; they were pretty close either against a double weakness or with a weather boost against a single weakness; Bullet Seed finally pulled ahead with a weather boost against a double weakness. Bullet Seed is just that bad a move.
I have not checked, but with the change to 1.6x type advantage, Bullet Seed might come out ahead more often against a wider range of targets weak to grass.