The problem with melee cones in my opinion, is that for melee ATs, the most efficient way to use them usually means playing to the least efficient way for melee ATs to play.
For example, NPCs surrounding a brute tend to cluster 1–2 layers around the player. As soon as the player tries to jump outside of the group to line up a cone, NPCs will start moving around again making it difficult to line them up. If cones were wider and had shorter range, then at least it wouldn't be a struggle to hit more than 2 NPCs more reliably. You wouldn't even have to adjust damage numbers so long as you kept the area close to the same square footage.