I don't think PI is broken. AWD is easier to drive, but I don't think it's faster (in the hands of a good driver). Select cars get the lions share of the tuning attention.
But I do agree there is a problem.
My feeling: The hoppers should restrict downloaded tuning setups if they affect tru-skill (which is basically all of them, afaik).
Ie, if you didn't tune it yourself, you race stock. I would be happy because I enjoy tuning the cars - even though I don't really know what I'm doing, and probably only manage a few 10ths at best. If I put the effort in (and it *is* a lot of effort), I should be rewarded with a higher ranking.
As someone mentioned earlier, downloading a perfected car feels like cheating. Which it is, in a way.
I know turn 10 had great intentions with the storefront - And it works brilliantly for designs, photos, etc. But tuning is different. The point of the storefront is to share and learn. You can see and learn from a great design - you can't from a locked setup.
Finally,
I feel the irony is that downloadable setups have leeched originality and variety from the online game. There is far less variation, as so many are stuck driving the same cars.
I exclusively drive A class online, I've hit level 50 a while ago and have a ~25 ranking. So I feel I've played a lot of races.
I have four main cars, two AWD, two RWD. In all my online racing I've seen two other Gallardo S's (mine is RWD), an occasional Audi RS4's and not a single Saab Turbo-X (which has the most amazing sound - I highly recommend messing with it)
It's sad really, yet I've seen 100s, if not 1,000s of S5s and LP640s.