The main problem is that CoH2 is programmed very poorly. It could have way better FPS even without DX12 if it wasn't implemented the way it is.
I have a GTX970 and a brand new i5 and still I lag after a US phosphor barrage.
But you do realize that almost no game at all supports it?
Whoever is without sin casts the first stone.
Someone has to start my dear Katitof.
And in addition vCoH implemented DX10 with a major update (OF) that brought many new effects.
So it is possible.