I think the A7R AF is super accurate.
I say this as a previous owner of the 5D2 and 5D3.
As mystik610 has alluded - this is due to the A7R's use of contrast detect AF; it's rarely that fast, but it is accurate. Phase detection can/should be much faster, but can be less accurate (hence the existence of AFMA [autofocus micro adjustment] on some DSLR bodies). In theory, a DSLR focussing using LiveView should be just as accurate, but slower (as it'll also be using contrast AF).
There are exceptions - such as the 70D with its dual pixel phase AF system in LiveView. It's faster than contrast detect, and shouldn't suffer from the usual phase problems where the AF sensor is separate to the image sensor.