No, I'm not sure it's an issue with P+ but rather something deeper. For example, no matter who the player is, the CPU will always charge forward at kick-off. The "intelligence" part appears absent from "AI;" P+ seems to only influence abilities and outcomes.
It seems to be similar when the CPU has possession in the final third: they predictably and regulary make poor choices between whether to pass, shoot, or take on a defender; their stats, however, influence only whether they are successful or not.
I don't see a great difference in how CPU players "think," only in their outcomes. If there is a variety in decision making built into FIFA, it's not nearly emphasized enough. The new Vision upgrade seems intended to change this but I doubt it'll be enough. Vision, after all, is only one of many mental factors involved.
What makes things that more difficult comparing the AI from different years is that changes in gameplay mechanics confound the issue. In particular, changes in tackling and defending made playing defense in 11 a breeze. So, how much is that the fault of the AI, and how much is the fault of over-powered tackling?
It will be interesting to see but changes to defending for 12 should have some major implications for what it feels like to play against the AI, at least at the individual level, not team AI. Of course, that will all count for little if other imbalances remain, like CPU response times and their ability to dribble and/or defend unrealistically well.
I think it's certainly true that something was wrong with custom tactics in 11, and maybe P+ has a negative influence, but I don't think P+ is the primary cause. P+ was intended to emphasize a range in abilities, but when the level of intelligence is so poor at the highest level of that range, the range itself cannot be great, and thus there is little variety.