Johan said they made the AI "dumber" as it was too opportunistic and aggressive. I read that as him saying it'd be too much for new players (which is the entire playerbase right now), and they'll slowly improve the AI as the game progresses and more people become familiar with it.EU4 was really easy on release. You could basically auto PU other countries just by marrying them and then doing a claim war.
Imperator looks pretty easy so far but there's no reason why that can't change. If people want more challenge, there will be more challenge.