R1 tyres and R2 on cars that do not allow R1 are Qualify tyres.
If you cant run 20laps on R3s in a GTR in LFS it means you are pushing too hard and over driving the tyres. I have run 20+ laps R2 fronts and R3 rears on Aston with no issues. No pitstop and ALL tyres still green at the end of the race.
Yes the Aussie V8s run huge cambre to allow the cars to turn BUT when you watch pedal cam in the cars you realise it takes then up to 2 seconds coming out of a corner in 2nd to feed power until their foot is planted. Winning is about modding your car so its better, always has been and always will be.
People in LFS constantly foot mash and use car setups with stupid unrealistic values (But fast due to physics holes) and then wonder why their car/tyres suffer. As more damage comes in it will force more realistic setups.
The tyres in LFS are off but not by what you say, probably more your driving TBH.
I really really doubt that GT5 is near realistic. Its a mass market pokemon (Gotta get em all) car collection and mod game, not a sim.