I'm glad they've acknowledged the problem. Not surprisingly, there wasn't much talk about this problem since a vast majority of users don't use flash in low light with the 5D Mark III. And the ones that denied this thought it was normal since they had nothing to compare it to. I thought I was the only one having this issue when my 5D (original) was locking on instantly with the AF assist compared to the 5D3.
I found this to be a major problem at a recent function I shot at. Without flash my Sigma 85 f1.4 focus near instantly but with AF assist beam it took half a second to respond and then hunted a little before locking. It got a little awkward for me since I was thinking my gear was playing up. Never thought I would still opt for >50% use of my 5d2 after I bought a 5d3. Without flash though, the 5d3 absolutely killed the 5d2 in every way. It takes longer to work out how to use it, but as a professional tool, you should be more than willing to customise and learn your gear properly.