Indeed.Most of the detail in the trees in Crysis 1 come from textures, not polygons, and textures have filtering instead of AA, so that solves that problem. They also don't have branches as thin as the ones you see in Tomb Raider. It's not entirely about amount of detail, but the size of that detail as well. The branches are often 1 pixel or less in thickness, so without AA, the detail can't be rendered very accurately, so it appears to jump substantially and even pop in and out of visibility on some pixels. Post AA then makes the problem worse by assuming it knows about the edges, when what it's seeing is mostly noise, so it alters the image in a way that makes the shimmering even more noticeable.
From traditional post AA solutions FXAA is actually best for such flickering mess as it has option to reduce brightness of single pixel detail and thus reduce the flickering a bit. (1x MLAA/SMAA doesn't do a thing to a help with a single pixel detail.)
Not sure what they could have done to improve trees as they apparently did use deferred renderer for opaque geometry, could be that TAA would have been the only 'easy' solution. (Or something like adding extra bit or two for a pixel which tells post AA that blur this pixel to hell and back when it gets too lonely or far away.. (Perhaps do part of this blurring G-buffer?))