Tuning at least for GR1, 2 , 3 & 4 don't make you so much faster. A good tune will let you more comfortable at the wheel , making less mistakes and at the end able to finish a 10 laps race at a good regular pace.
Even if they don't allow downforce and suspension tuning , they have to open the LSD settings. A simple tweak will let you more confident out corner under acceleration, this would be already a great thing.
100%.
I'll concede that tuning may make a difficult to drive car ~several tenths a lap quicker(than PD's tune)... which will put it on pace with the "meta car for that specific track"... it will not make it a meta car... just competitive. On the other hand, tuning a meta car on the track that it is already meta on, is not going to gain much, it is not going to be the difference maker in a 10 lap race... on a 1 lap shootout, maybe, but not at race pace and taking alternate lines while battling/defending position... those few 10ths/100ths will be negated by decision making/racecraft.
Then, instead of seeing a grid dominated by "meta" you would see a nice mix.
I gravitate towards the 991 because it is setup perfect for my driving style (car is plain good as delivered by PD, and I think that is why you see so many)... but I can make the 458 (a seldom seen and delicate car) run just as predictable, thus nearly matching my times. Love the Aston, just needs some LSD love, Jag needs turn in... the list goes on... none of the cars are suddenly going to be "on rails"...
I've always said leave weight/hp/aero/ride-height to PD's BoP formula, allow us chassis, LSD and trans tuning... and, trans tuning is not going to suddenly give a car "more top speed", most do not hit the limiter now... they run out of power before they run out of revs...
most...
Those that don't want to tune can run the "meta cars" (they will still be meta tuned or not), those that do want to tune, can spiffy up and run the "non-competitive" cars.
I understand the "no tuning" folks, and all the reasons for no tuning they present, but, to be fair, there are a bunch of folks that really geek out on the math/testing to make a car run predictably.
Reflecting...
Maybe in the shorter races, tuning should stay prohibited... as with tire wear being set to none, tuning would benefit silly castor/camber settings... in races with tire wear on, if you run exaggerated caster/camber settings you are going to be in the pits a bunch, or fighting the car after a couple laps... loosing time in either situation.
More reflection...
Maybe PD allows a tuning... but limits it to within 10% (or some random factor) of the PD tune, and limits final drive in the trans, but allows ratios revised... that way you can make little tweaks, and avoid ridiculous tunes that folks mention... and not gain any top end speed... while leaving weight/hp/aero/ride-height to PD's BoP formula intact...
Wishing...
I don't know.
But as a math/engineer/geek it seems a shame to not be able to use that skillset in a race when it is available both in the game, and utilized in the real world.
Reality...
I know, comparing to the real world is tough in game land...