Consensus on 24-70/2.8 II field curvature at infinity focus?

I suspect you are right and I rather doubt Canon did design this lens with landscape photographers primarily in mind. I know that the original brief for the original 24-70/2.8L and its 28-70/2.8 predecessor was to produce a fast zoom for photojournalist use and I doubt that brief has changed significantly with the MkII. As such some field curvature at infinity would probably be considered a reasonable trade off against other performance characteristics that a photojournalist might consider more important.

Yes, that's what I start to think as well. However, the major increase of field curvature when focusing at infinity was a surprise.

I'm certainly not implying this is the case with you but I fear some photographers do buy lenses because they are the fastest or most expensive, rather than with a realistic assessment of what they are actually going to use the lens for, and so can end up making expensive mistakes, perhaps like this. It would be nice if a manufacturer could list all the things a lens is not so good at but naive and unrealistic to expect that of course. In the meantime we rely on test reviews and hope the reviewer is able to cover the aspect we are particularly interested in.

I upgraded partly because of the much more convenient size of this lens. The design of the old one was a bit annoying in comparison. Also, the sharpness seen in reviews was just as important as a factor, but resolution tests shot at a few metres obviously say *even less* about curvature at infinity than I would have expected. Note to self: next time, test before buying at genuine infinity rather than e.g. 10 m.

Yet another technical hypothesis I made was the following: since phase detection AF relies on light passing close to the edges of the lens, chromatic aberration will supposedly make AF ambiguous, meaning that the AF system can front-focus or rear-focus depending on the colour of the subject. A lens having less CA (read: 24-70 II compared to the original) should, technically, also have more consistent and accurate AF. I noticed this also with the 24 f/1.4 II vs the original version. Less CA, more consistent AF.

More consistent AF in itself can be reason enough to upgrade. I wasn't happy with the inconsistency of the original 24-70. I don't care about CA otherwise, since it is easily processed away in Lightroom, but I do suppose it matters for AF consistency.