You have to think that as of XY it will probably set its hazards and Baton Pass some boosts, namely Agility and Swords Dance. In BW this would have been a totally outclassed role with better abusers in NU. Then Scolipede got Speed Boost. Bye bro. The thing is that Leavanny isn't supposed to sweep. Even in permasun with Chlorophyll it's rather disappointing. As I said before it will probably find its role as an offensive support mon, a role which could be well filled by Scolipede in the past. Leavanny just has to pick its moments. As you have said, Leavanny isn't amazing, but it will fill a role that will be lacking at the moment. Strictly speaking it's one of the most threatening Sticky Web users with Galvantula. So it may get to see more light in upper tiers too.