I bet the YZ-2 will work very well in all conditions not requiring a gear cover so to speak, i. e. everthing except very dusty dirt tracks, and even there it might work with a shorty battery to the rear, the ESC mounted on the battery strap to increase chassis roll, and some brass rear suspension mounts. I don't know if weight distribution is so much different to the KF and the converted 4WDs when running with saddles, the centre of the car is crammed with stuff up to the servo in the front in all three designs. At least the Yokomo does away with a belt and eliminates torque steer, that is why I fell in love with this new YZ incarnation right from the start.
With my Thunder Power saddle packs, I don't see any issues regarding the battery strap. Their connectors are way more outside than those of the Yokomo packs.
The 3-gear B5M is not tailored to high-grip surfaces but rather to stock racing. Don't forget that 17.5 turn blinky racing is huge in the US, and 'stock' racers want/need to shave off every single gram of (rotating) mass to be competitive, hence the lightweight MIP puck drives, aluminum topshafts, slipper eliminators etc.