It's the ICE aspect. Driving ICE after driving an EV is like having an analog television instead of HDTV. The vehicle doesn't suck, but it's not on the same level as an EV.
The new F66 overall is pretty nice. I think the new interior materials are actually nice, and the overall driving experience is very MINI. The new infotainment system is really good, except there are some annoyances with touchscreen control. My only real hatred is the "Go Kart" experience fills the car with fake engine noises that are even louder than the actual ICE engine. So whatever handling differences there might be are unusable in my opinion since the fake noises are so detrimental. Even with that, I felt the F66 handled better than most other cars on the road.
I suspect the J01 is probably a very nice car, but isn't going to handle as superbly as the F56 SE.