It is surprising to some extent. It also explains why some reviewers say it feels lighter than the F8X while others say it feels heavy since its around 4K lbs. The weight difference is small enough that other aspects as chassis tuning and responsiveness play more of a role of the feel than the absolute weight. Some think they know its heavy and are biased to confirm a heavy feel while others are more open minded and dont feel its heavier at all.
I think the weight comments are mostly coming from the sheer size of the car. The car is going to feel like its heavier because of the length of the wheelbase. For example my M2 feels a lot more playful than my M3 did (Both are comps). The main difference, the wheelbase. The G8X is simply bigger inside and out, so it would feel heavier as you’re moving more mass around.
The other aspect is that the G8X does in fact weigh more than the F8X. I know that when I have a passenger in my car, the dynamics shift. So yes, you’re going to feel a difference between the cars if you’re on track or even spirited driving. However, in like 70% of the time when you’re not driving like an A-hole, I honestly don’t think you’ll notice any difference at all.