Less powerful, but more than enough for milling. A 2560 is great for 3d printing because the files are so big (and fast), but every implementation of GRBL runs on the uno/nano, even ESTLcam runs on a nano.
With that said, it will work fine for the mpcnc (drivers are kind of overkill) and grbl is very well developed. Software like bCNC is really close to Mach 3 in functionality too.