Below I share ten 100% crops from one of the more-formal focus tests I performed. The subject is a large book properly aligned with the camera at a relatively close focus distance. Starting with a slightly defocused lens, each shot was autofocused using the center AF point that was very comfortably and completely covered by the book. The first 5 and last 5 images from this particular test are presented below and are representative of the larger test group. … The camera was a tripod-mounted EOS 5D Mark III with mirror lockup and the 2-sec self-timer in use.
Of those 10 shots, 4 are sufficiently OOF as to be unusable (3, 4, 6, 10). A 60% hit rate with a static subject and a tripod-mounted camera, particularly one with an excellent AF system, does not inspire confidence.
Also, this is a departure from the norm for Bryan's lens tests (and one, frankly, with which I'm not too pleased):
My evaluation lens was a short term loan from Sigma, as they offered the production-grade lens before it was commercially available.
Any time a manufacturer supplies a product to a well-known reviewer, a big unanswered question is whether the provided copy is truly representative of units purchased retail. Clearly, it would be in Sigma's best interest to pre-test a batch of them and pick the best copy they can find for review (in fact, they are supposed to generate measured MTFs for every lens they produce, so they have the data already).
I've always felt that one of the strengths of Bryan's reviews (in addition to their thoroughness and readability) is that he purchases review copies through standard retail channels (B&H may put him near the top of the preorder queue, but that's fine), and therefore avoids the potential confound of bias introduced by testing a 'hand-picked' lens from the manufacturer. I hope Bryan chooses to test one or more copies of the lens purchased retail to see if the results align with the copy provided by Sigma.
I don't disagree with what you are saying at all, but I understand the conundrum as a reviewer. These days it seems like most reviews are published before retail copies are technically available. Waiting until the lens launches to the public means that you lose the early momentum/hits that are so important to building a brand and a website.
I don't have an "in" with Sigma, so I am waiting for a copy to be provided to me from a retailer for review right now...and it's taking a while.
P.S. Your point about the AF is very well and clearly stated. That's a problem...and not a small one, particularly if one intends to use this lens commercially. You could by with it doing portraiture, but certainly not event work.