The problem is, tuning is really about tailoring to your driving style. I ran with some quick guys in GT6. We'd run Lotus Elise 500pp (if I remember correctly) and our tunes were night and day different but achieved the same goal. We stabilised the crap out of it and it became OP as hell in lobbies.
All tuning will do is make BOP ineffective, open up exploits and produce new OP cars, while killing the characteristics of each car. The Elise I mentioned above no longer felt like an MR by the time it was tuned. You could make most cars behave the same, which then took away cars feeling different and having their own character.
It was tough learning the 458 GR3 and I was desperate to change front spring rates, tweak the diff and toe. After a few weeks, I fast with it now and it doesn't need a tune.
Base tune tweaking should be left to PD, but then if they fundamentally change a car someone has mastered so it feels very different, just because someone else feels it's to difficult, isn't fair on the person learning a cars traits(?)