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Don't threaten me here)). It's not useless, there are just many much better skills than diplomacy. It doesn't take priority. I don't really understand how it can help at all. I don't think the opponent will offer you a surrender... Especially if it also costs little. It's completely pointless for them. And creatures don't always join you as you want. For example, 6 creatures from a Rampart might join your full stack. And you only have 2 dragons. Will you take the creatures? I think they won't be useful, they'll only lower morale, and besides, you won't have enough of them even for a couple of weeks, but you can grow the same number of dragons in a couple of weeks.
But of course, you can try it)))