I selected scripted weather, set it up for rain. Go on track (Mills) in the Megane. Its raining. I put wet tires, and can do a lap times in low 1.08. Then I go to main menu, set sunny weather. Go back on track and can do only high 1.09. I can feel the difference, there is clearly easier to drive with wet tires on wet track than with slicks on dry. Something is seriously wrong.
Same thing for me, I don't remember my time but I was 2 sec slower than IA on dry track and 2 sec faster than IA on wet tracks... The grip with wet tires is really high, I think too high to be realistic
I seem to recall the devs commenting that they are aware of the problem and it will be fixed in the future.