To be honest, it just doesn't have the necessary defenses to be a good rain tank.
It also has weaknesses to Fighting and Rock, which are now two common type moves (ex. Close Combat, Rock Slide, Stone Edge, Brick Break, etc). It also takes a supereffective Volt Switch, which is also quite common.
Outside of being a rain tank, it has limited potential.
However, it still is great in NU and maybe RU.