The AI certainly needs more work. In all my single-player games I've played as Geralt and won by a mile to the AI players, as can be seen on the attached screenshot. The main AI problems seem to be:
1) Poor quest priorities, resulting in wasting time collecting non-essential leads (like purple leads, when the quest needs blue and red).
2) Doesn't properly prepare for obstacles, which results in losing most dice rolls, and as a consequence gets drowned in wounds and foul fate tokens. As the game is designed to punish players who are too aggressive, and don't prepare properly, this is what is happening to the AI players. As such the AI needs to be less aggressive and better use its development cards.