The 2012 Atomic FIS SL were the older D2 design. Lots of edge grip and very stiff. The new gen from 2013 onward are lot more fun and much more versatile outside the gates.
I have the ones without the D2 thingy on the top
(like these) and I recall someone saying back then that they are bit more approachable than the ones having those.
Anyway, for the sake of science and comparison I went and bought a pair of Head WC Rebels e-SL RD FIS 165 (2021) and tried them first time today. Skied parallel slalom style courses but cannot really compare to Atomics yet as the conditions were much softer than the winter this far. Seemed to work very similarly though, perhaps a bit easier to initiate the turn.
Interestingly, the boot center on Head is about an inch forward compared to Atomic which I would have guessed to notice more on the snow. Also, a bit surprisingly, Head is significantly stiffer throughout the ski when hand flexing it. Looking forward to test them on some proper ice!