Mugen have their own forum with which the very people who designed the kit will answer your questions? Mugen have gone out of their way to help the people that have bought their kits get better results by providing an easy to use area where you can access tons of setups from complete beginners to the top sponsored guys?
Mugen, not THIRD to anyone... maybe
Sorry for that, but some people really need to remove heads from certain areas of their being.
*From what ive read from other people* the Mugen performs well if your aggressive with it. The XB8TQ prefers to be driven correctly and will reward you for it.
Someone else may have a completely different perspective on how their kit has gone, i dont know and you shouldnt take the above as being 100% accurate.
Personally i would have thought that you should be able to get the handling characteristics that your looking for from any top level buggy, the further down the scale you go the more fixed in their ways they'll be, but the good kits should allow you to really dial it in however you like to drive.
Im suprised you've not been able to get what you want from the Losi, but hope you have better luck finding something that suits your requirements