Friend has that lens and I've used it quite a few times. It was worse than AF microadjustment on his 6D. The problem was more like lens failing to stop the AF motor after nailing focus. So it'd both front/back focus quite often, depending on which side the lens was focusing from.
Heard the exact same behavior from a few other people as well. Lens was from one of the earlier production batches, so maybe that explains it.
I wouldn't want that lens even if the AF was reliable though. If I'm carrying around a 1kg lens, it's not going to be a 50/1.4. For someone else that might be OK but not for me.
With the weight you're right, it's absurd - but most of the Art lenses are hefty.
Mine is 014, so also an early copy - firmware for Nikon is 1.00. Canon got 1.01, as well as the genuine Sigma mount - but that's just to become compatible with their MC-11 converter for Sony.
I took just ∼180 shots in my room with this and other lenses. The "flicker" warning of the D850 was often on, so take my findings with some grains of salt (not just one). My lens needs +6 AFMA, and internally it's +3, +2, 0, -2 (for 0.45, 0.8, 2 m and ∞ ). I usually set AF to AF-C and single point. AFMA beyond camera possibility? I would send the lens back. The dock is nice for fine tunings, but the more off it gets, the more problems the AF-module will create. Like driving a car with a mirror which looks 2 m right of the street..
AF center point: 1 out of 20 shots was a bit front focus, the others spot on.
AF extreme corners: depending of the corner, upper right was worst, hardly one shot in focus, the other corners were better. Using LV didn't show a bad lens, I just learnt: in tungsten light better no corners to AF. I think it's a DSLR problem, maybe even a Nikon, don't know, it's just a bit disappointing. There's a possibility the AF module is misaligned due to a fall, but other lenses were better - partly much better on the corners of the AF pattern.
Then I tried the same game with D810. Again, nearly no AF problems when staying on the center, but the outer corners / borders remain a bad idea to do. For me, with AF-C and my maybe insufficient AF-skills, that is.
Along the other lenses were two Nikkors: 85/1.4G and Micro Nikkor 105/2.8. The Micro Nikkor hardly misses but at the corners it's also more on the uncertain side of things. The 85... well, now I don't wonder anymore about focus pane on the wrong spot And the Sigma usually is better resolving than the Micro Nikkor. (lenscore.org confirms that with 1001 against 1160 points resolution / 961 against 1053 total points)
Back to the 50 Art. I will not exchange it for the much lighter 50/1.4G, in fact I got rid of that when the Sigma came out. Sharpness wide open still is incredible, so for me, if it has to be a 50 mm, i don't see a point in constantly thinking "neat, but with the Sigma it would have been really good" I can't speak for any other 50 mm Art, but mine is close to perfect with center AF on PDAF.
Against the unreliable focus: I'm afraid the medicine's comes in a package with a big SONY logo and the number A7RIII on it.
Okay, neither the Sigma nor the Sony are something for toni's definition of "winning team", but others might find it useful to know.