It's not that Elephants are unstoppable. Dual bless is great, except that you either sleep your pretender or take bad scales or both. Meaning you have to commit a higher % of your resources to kill his elephants, while you beats you by simply having better scales or more research or both.
I'm not sure what you mean by Vanheim. Although they are a ridiculously powerful nation, trampling is the one thing that really messes them up. I think the reason people talk about elephants so much is because they require no strategy. Oh look, elephants. Build a fortress in that province, all of a sudden you can make 7-8 elephants per turn. Look at me I'm a master tactician.
