Actually, it was the Shapeoko 1 which introduces the idea of belts (MXL), then switching to Gates GT2 belts with the SO2 (ob. discl., I got a free machine for doing the instructions, see Github). Since it was opensource, the X-Carve was forked from the SO2, though the X-Carve Pro was a completely new design.

Note that belts were continued through the Shapeoko 3 (I got a machine as a "thank you"), though the Z-axis got a leadscrew in the Z-Plus upgrade, then the Pro (since, I got a job with the company and got an XXL as part of my employment), then the 4 (the original Pro is referred to as a 4 Pro sometimes), and it is only with the 5 pro that ball screws were switched to for all axes (and I now have a 5 Pro).

For an example of what a belt-drive CNC can do see:

https://community.carbide3d.com/t/hardcore-aluminum-milling-...