But it's annoying to buy a fairly expensive AF lens which you're expected to fiddle around with on a docking station and even then seems best used, in the case of many copies at any rate, in MF mode.
Why do you think AFMA exists on Canon cameras? To address the same problem that the docking station is for.
The problem isn't QC it is engineering tolerances and the fact that neither camera nor lens are all made the same. There is copy variation between each camera and lens. This means that whilst AFMA might be +5 for a given lens on your camera, that same lens might be -5 on my camera and that same lens might be +0 on someone else's camera.
I don't disagree with any of that (to the extent you're talking about AFMA adjustments rather than inconsistency). My comment wasn't specifically about Sigma, though it seems more of their lenses need adjusting than others and more of them focus inconsistently within any given AFMA tweak. But after using a variety of mirrorless cameras over the past 18 months, where AFMA simply isn't an issue, I'm getting less tolerant of/patient with this aspect of dslr technology. As for inconsistency within any given AFMA adjustment, presumably mirrorless isn't helpful, but manual focusing avoids that and mirrorless cameras make manual focusing easy (I recently bought an EF-mount version of the excellent Sigma 70mm macro and have been using it on my A7r rather than my 5DIII - so no focusing problems at all aside from incompetence at my end...).