It's been highlighted at Bnet forum.

it could be due to the high res mouse
it could due to the fact that even if you disabled mouse acceleration in SC2, the mouse acceleration in macOS is still in effect.

i havent try cheapo wired mouse yet

im using razer orochi, and notice that u need to change some option in razer preferences..what i always do is, i just uncheck the 'Enable Acceleration' box, then check the box back, then wohoo the mouse back to normal..but i need to do it every time i boot into mac, which is quite annoying..dunno if there are special way to overcome the prob.