I have the Sigma 50mm Art and 70D, and I love that combination. So far, there is no autofocus lens that offers higher image quality than the Sigma Art, between 45 and 55mm.
Yes, some bodies of camera do not communicate perfectly with the Sigma, resulting in inconsistent focus, but my 70D works well, and in the event of preblemas, the live view works wonderfully because of the Dual Pixel AF.
I had a Canon 50mm F1.4 and was never satisfied with the sharpness, contrast, and longitudinal chromatic aberration when more open than F2. In fact, it was necessary to stop down to F2.8 to achieve sharpness and contrast similar to Sigma 50 Art in F1.4.
Even my Sigma 30mm Art overcomes the image quality of the old Canon 50mm F1.4 when wide open.
The fundamental point is that Sigma 50 Art has no chromatic aberration, even at F1.4, and this was only achieved by Zeiss Otus 55mm, which has only manual focus.