While I'll agree that the PP system is flawed it does an ok job of an extremely complicated task and allows a greater level of freedom of car choice and tuning. Most importantly, whether one likes or dislikes the system, it's the one we're all stuck with.
Sark
Surely its not very accurate sometimes but its a good way to try to equalise cars in a race.
Power/weight limit is far worse because there are other factors that determine car's performance besides power and weight.
I don't mind very mild tuning, but what I dislike is that in some cases detuning is needed if you want to use a car that you feel fits in that event, but it doesn't. That is something that I completely disagree with and it is unnecessary. This is was more noticeable in Seasonals (in GT5 specifically. Not yet in GT6) were people just took a race car and lowered the PP and still got better times than any street car could. Proof that the concept is flawed and serves no useful limiting purpose.
Some cars like the Veyron and Huayra are rendered useless in most events were they could easily participate, like the Super Car Events. In other cases, some cars fall very short against the competition and you're unfortunately forced to tune them.
I certainly wouldn't mind PP if there were different PP range races per event, much like in GT5's Seasonals. This career mode is far better than GT5's, but there are so many cars and so many possibilities, that the PP system only limits the car selection for those of us who follow the closest-to-stock style, as I imagine it does for those who prefer the fully tuned style.
I think I mentioned it before, but why not three sets of events for let's say, the European, American and Japanese Car events? Starting with three races with a range of 350-450pp, another set of three races with ranges from 500-600pp and one last for 650 and above? Same goes for Turbo events, NA events, FR, FF, AWD, MR...
If PD did this, I wouldn't hate the PP system, we would have bigger career mode and I would happily agree with you two.