Same here. I think its mostly the damage but, in GT Sport people must take care or they are penalized. A penalty in a short race is painful. Even if they get it wrong 30% of the time, its right 70%. In iRacing the only penalty is a licence rating hit, which many times is inconsequential. Either way, its amazing that the less invested crowd seems to drive more carefully.
Unfortunately, the change in tire models effect the lap times a lot... and depending on your driving style, it affects some more than others.
+ I feel a difference going from from g27 /csw v2 + gt27 pedals to DD1 + CSP v3 (mostly in braking)
Would be cool to track how over the years everything affected my speed but it is hard to replicate same conditions