You've got a point there about the Porrari being sluggish, but please keep in mind what cars you're comparing it too. The Lx6 and RAC are VERY small weight/high powered cars. They're bound to be responsive and such.
The Porrari on the other hand... well yeah, it is heavy, and that's exactly what it feels like. My point is that if you compared the FZ50 to cars of similiar power/weight ratios I don't think it would seem so "boaty".
I used to be an LX6 maniac back in S1, I still enjoy it. But I've learned to enjoy the Porrari as well... all it takes is a good setup and a few laps. trust me, it's worth the try. I'm attaching my favourit set: