They aren't magical at all... Wouldn't you be scared if an orc suddenly roared next to you?:D And let's consider the effect of the horde's rage as the target unit's heart bursting from such screams... :) And what's so magical about that? And if you mean balance, I don't think one rage ability will replace magic;)
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In the original, this scream is called "fear my roar." I really like it. Especially when taking cities - I would always roar at the archers, and they never fired a single shot, poor things. And then the cyclops waddled up to them, and that was it. )))