And those are not even the "normal" Cup 2 R tires, it's MB's own special tire with an even softer compound. It's more like Cup 2 RR in terms of grip. You can see that really clearly when looking at the max cornering G and the braking distances. That's all down to tire grip and downforce - and with 400kg of downforce (at 250km/h) the GT BS is not that much above rivals. GT3RS has 313kg, GT2RS 289kg, Huracan STO 360kg, 765LT 302kg and so on. So yeah, it has a bit more, but it's also a lot heavier. In this case I would say the tire is the deciding factor.
I do wonder what's gonna happen on that front as well. The tires have been getting more and more extreme but it's making less and less sense. The tire you would pick for daily driving would be the PS4S. It still has very good grip, very good handling, but also very good wet performance, doesn't wear out quickly and doesn't cost a fortune. But we are so many steps beyond that now. You can now get the Cup 2 for your track tire... But then that's not enough, so you can get the Cup 2 R. But then that's still not enough and every manufacturer is now coming out with their own special version of that, trying to squeeze out every last bit of performance they can - even though the only thing these tires are good for is setting a lap time for a magazine and are even designed to give the best performance on lap one (which is like 1s faster), with the performance dropping for the rest of the laps. It might not be long before some manufacturer demands a tire from Michelin (or anyone) that's as fast as a slick, but disintegrates after one lap. And what exactly will that lap time show? That's anyone's guess.