[Universal Creations]

I tested both the Sigma 85 Art and Canon 85/1.4L with multiple samples and camera's (5D3/5D4/1DX2) and the Sigma is more accurate at close distance and faster in low light. At outer focuspoints the Canon starts to hunt, but not the Sigma. So no, the Canon isn't better at focussing than the Sigma.

Btw: there is nothing wrong with the IS of your sample: they all aren't as effective as Canon claims. I could only manage to get around 2.5-3 stops.