You just need to know how to handle slicks in the wet and you'll be fine. There is no problem with AI in the wet anymore. The people still moaning about it are most likely just not good at driving in the wet. It takes time if you're not used to it.
Don't treat the tyres like other games, where you back off and take it easier when you're losing grip. The tyre simulation in Pcars is the closest to real life I've ever experienced.
When the rain starts coming down, the track surface cools very quickly. This cools the tyres. The slicks are made, like real slicks, to operate in a certain temperature range. If you take it too easy when the track is getting wet and cooling, your tyres will drop out of their operating window very quickly, which will make it near impossible to drive, as without track temp, you won't be able to get the tyres back into their window, so they won't bite into the surface.
What I do, is as soon as I see rain drops, I'll start really leaning hard on the tyres in corners. Braking late and accelerating hard, to put as much heat into the tyres as I can. This way, my tyres will take much longer to cool down, and I'll keep them in their window a lot longer. I usually don't need to pit until the same lap, or a lap later, than the AI drivers.
I'll also add that I play on 90 - 100%, so I'm not racing against easy AI.