To be fair the AI in the vast majority of strategy games is poor. Given the complexity of HOI the best we can reasonably expect is that it doesn't do anything too stupid or is too easily exploited. If you're looking for a challenge from the AI, you shouldn't hold your breath.
But in the other HoI, we had challenge against AI. Even if it was not really smart (but not stupid either). So, I think we can expect challenge in single player. And we're talking about a Paradox game, not a Civilization.
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