Nah man, the relative performance in DX12 has certainly gone up. There's bigger disparity in DX12 titles compared to 980Ti than there is in DX11 titles. It's quite noticeable. DX12 has nothing to do with clockspeed. :/
Your little thumbs down is super petty, holy crap.
Anyways, ignoring that, as I said above, check the benchmarks. Performance disparity between Maxwell is higher in DX12 titles. I know some of you really dont want to believe it, but it's true.
I think you two are probably most partially correct in the manner of speaking.
Nvidia hasn't really improve on addressing the dx12, but they introduced a workaround instead (around to reviews).
Think of it like and rpg...dx12 is an area that both vendors have to go pass to reach the other side:
-AMD Fury X take 10 seconds to go directly through the dx12 to reach the other side.
-Nvidia 980Ti taking the same path takes them 20 seconds to push through and reach the other side due to being less equipped.
-Nvidia 1080 trade off some of the strength on brute force for agility for dashing/running speed instead, and take a slight detour to avoid the heavy traffic/large number of mobs. Due to meeting with less resistance, it ends up taking them only 15 seconds to reach the other side, which is less time it than to charge through the dx12 path like the 980Ti does.
So basically Nvidia decided it is better (for them cost wise) to invest on better running shoes to go around the dx12 mobs, than to equip its soldiers with weapons that enable to them slash down the dx12 mobs as quickly as AMD does.
Weird analogy I know, but I hope it make sense