It really differs a lot from 14 - 135mm. ALL are used a lot at infinity and far away in typical landscape and nightscape pics.. The 50, 85 and 135 are used also at typical half portrait and face portrait distances. The 14 and 20mm in club and music environments. For my 5d3 and 7d2 I had different MFA setting using the dock for the 3 distance ranges and had good results. Now with the eos r it is better still. Now I feel even more secure to use them fully opened even in dim environments. I only had one art that was not good - not from the focus point of view but the corners were not of the same quality - maybe decentered. I tested it with stars at infinity and they looked quite differently in the 4 corner. Got a new copy which was much better in that respect. As I said before I also updated the firmware when available. This may also play a role. I owened also the Canon ef 50 and 85 L lenses and was never that happy. The 50mm showed too much spherical aberration incl. the focus shift and the focus speed of the 85 was often too slow. Also the focus by wire implementation was not to my taste.I've had the ef 50mm f/1.4 USM for years. Not nearly as sharp as the Sigma, for sure, but nails AF quickly and reliably, even after the scorching summer I left it (by mistake!) in my car parked in the driveway.
By the way, nubu, do you often use the Sigma Arts wide-open from within six to ten feet of the subject? Just curious about how you use yours.