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Well, I wouldn't say that Academy is difficult. There's a period when you have a lot of troops but not enough hero units, and during this period, the mage hero is the weakest.
And Academy heroes would always benefit from a powerful starting spell, which is another advantage of the Stronghold and Fortress. In the Chaos guild, it might not even appear.
And developing an Inferno faction isn't necessarily difficult, but it's very long and tedious.