When playing AM the CPU gets an attributes boost across the board. Basically they're overpowered, which makes up for their lack of AI when playing a human controlled team.
On AP the game plays truer to the ratings as no team gains an edge attributes wise. Where AP falls short is in the CPU's AI in terms of aggressiveness, decision making, etc. Their lack of AI makes the human slightly overpowered.
In saying all of that, I'm loving AP so far this year. I've won big at times, but have also lost games where it felt I couldn't do anything. I've only played "play now" games though and have yet to start my CFM. When I do, I may find I need the CPU to be more challenging.