I strongly believe this pkmn will be NU or PU, its just too slow to perform as a sweeper. And finds it outclassed as a defogger by Decidueye.
Lurantis finds itself badly outclassed by Serperior in just about every role it'd want to fulfill in OU. However, in RU it may be better than Servine due to its access to Defog and ability to be a Defogger capable of beating most Rockers while maintaining respectable offensive presence. It can also go Physical or Special with Leaf Storm depending on what your team needs.
It could have been good if it wasnt so damn slow.