Weight bias is only a small part of the equation when comparing cars. Suspension geometry, steering rack swing, etc., etc. will have as much, if not more input on the cars' feel. For example, I've driven many XB2's - none have anything approaching the level of steering of the YZ-2 so if you're finding the XB2 a handful on some of your tracks, the YZ will generally be twitchier with the new 3-gear CA car getting twitchier still.
The YZ-2 dirt car should more or less fall on the scale of feel between the current YZ and the B5FL. Probably closer to being a high-quality version of the B5FL, however, with the B5FL not really being that great a car on carpet/turf, you'll have to decide if you want to be the guinea pig and take a chance on using the YZ dirt car as a "low-grip" carpet car.