it's not heavy mate, it's heavier than LX, sure, but it's not heavy, it's a normal weight for a drift car, and the reason because you feel it "heavy" is just that it doesn't change directions like a house fly, and is slower than the LRF class you are used to...
I, when swapped for LX6, was always complaining about the lack of any inertia, and lightning fast reactions that I couldn't cope with at first, I was compensating by high speed entries and had a setup that was making the LX a bit more slippery on all 4 wheels, so the direction changes wouldn't be that instant...
I think you just have to get used to XRT, and if you feel the need for more power just try and stiffen the rear stabiliser, it will make sure you're sliding around more (not that it will give you extra power of course )