I think that gear ratios should be exempt from the ‘no tuning allowed’ events.
You should be able to adjust ratios in a fixed setup, mixed car event.
I tend to agree with you there, but this would also introduce another variable to the data PD is surely trying to collect, so I'm hoping they make the best of the data they're getting currently.
For current racing, I'm not sure it would be absolutely necessary, if the ratios were set appropriately for all cars, but some cars just have weird settings. Usually you have fixed settings in real life for GT3/GT4, and I wouldn't complain, if they had modelled a REAL car with accurate ratios, but does that Cayman really have this gearing? Drove it at Alsace today, and didn't even need 5th...? Also, some cars' 6th gear is too short so it tops out in slipstream. And that's with cars created by PD!
This also creates a problem for the BoP, because PD is basing the BoP at the moment e.g. on this Cayman with weird gear ratios. If they were to change this to shorter gears, the car will be faster, so they would have to rebalance it.
I actually would like to see them updating the BoP's every 2 weeks or so. They should have enough data to draw the necessary conclusions from that and it would reduce the feeling of having to use a certain car for a specific race to have a chance. It should need only a very small update to update the BoP, so it could be done on a regular basis. But watch for that outcry when they change it during a Nations/Manufacturers Cup. Everyone with a previously overpowered car will raise hell!
PS: They should also have a look at that Gr.4 Megane. At Bathurst one of these goes through T1 a second behind you and cleanly goes by before braking for T2. They're a good 10km/h faster down the straight than most other Gr.4 cars.