It's my guess for they reasoning, but in that case, they totally overdid it anyway. I really don't see, why you would need such a boost if you play alone, but not if you are playing with 3 friends. Except for Bless and Course there are no other differences between player and non-player chars. At least no of wich we know. And regarding our current knowledge, the boost is far to strong. The AP boost alone is the issue here, hardly anyone cares about the vitality boost I guess.
