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If you need an explanation as to why that's nonsense, I'll explain. Initially, the Fortress was designed to improve its creatures WITHOUT building an upgrade structure. And that was the point, and that's why it has great value! Why would I upgrade creatures in the Fortress when, by the time they're ready, it's unlikely I'll even need to upgrade them from there? It doesn't give any tempo advantage, if we're going by what you said. But upgrading a creature on the first level – that's tempo.