I can see in the latter design how you would suppress z-axis wobble in one dimension (the x) by having the z axis move vertically on either a plate or two shafts. The further apart the shafts, the less wobble I can see a problem with z-axis wobble in the y dimension, though. Eliminating it would require a reasonably stiff x-axis and minimal play in whatever the hot end is moving on in z.

I have seen a rather clever design that used a single z-axis stepper where the stepper was mounted at the top connected to two lead screws using a chain.