Let me say that if you are driving in a green track, it's very usual lost of traction and bad braking because of a dirty track without rubber, so you have a slippery track. As someone told you, put Weather option in "Scripted" and you could change real road to "Light/Medium/Heavy/Saturated rubbered" but not in all tracks, there are tracks with only "Green" available in the first practice. Driving in a Medium/Heavy rubbered track is much better and real, you'll find a very different feeling, a lot more grip
In fact, you are right, minimum cold pressures for these cars should be 170/180Kpa equal to 25/26 psi in dry conditions (1,8/1,85 bars). But I don't know exactly in Michelin tires, it depends from technical regulations in every competition.
Low pressures are very good to improve traction in slow turns, you get much more grip with low pressures, car drives more slow in reactions but in general you gain a lot of time because good traction is the key being fast, further you can drive with TC and ABS very low that improve your lap time. When you drive normal pressures or high pressures, you lose traction but is better in high-speed turns, in general response is much better and you gets more top speed, this is good but finally your lap times will be slower than with low pressures. I don't consider 140kpa a cheat, sim allows it. In fact in iRacing a lot of cars you go with 130/140kpa for the same reason, that's the minimum now in GT cars.
Well, if you decide to run "real" cold pressures I also suggest working on traction in your setup with soft springs and probably you'll need more aero downforce.