I don't know how it'd be a huge advantage in MMOs, but in Ragnarok the bots used a re-implementation of the client and custom servers tested for differences and

I don't know how it'd be a huge advantage in MMOs, but in Ragnarok the bots used a re-implementation of the client and custom servers tested for differences and culling of entities by the original game client to ban bots (as they'd try to interact with entities that should've been culled)