[Baalz]

Nah, the nations that would dominate would be those that have N/B mages (like Mictlan and Lanka), rain of toads is low enough to be fairly easy research, and blood slaves are the only resource you could really spam early. Wouldn't be terribly hard to lock down 3 or more people's caps pretty early - earlier than most nations could really put a domes up (with a little planning you can ignore water/fire domes, and spam through most of the others). You'd probably have to ban it and maybe a couple other spells as well.