Don't blame the Poison type for GameFreak's decision to let EVERYTHING learn Toxic. If Toxic was almost always exclusive to the Poison type you'd be singing a different tune.
Even now though Poison has quite a few useful resistances, can't be worn down with Toxic, and can lay/absorb Toxic Spikes. Plus they may be one of the few types that can hit Fairy for SE damage in the near future.
Poison is not a terrible type--see Ice for that; resists nothing (except itself) and is weak to...the things you really don't want to be weak to. And every Water type can learn your ****.