The game starts very smooth (without Vsync 80-100 FPS) but over time the performance drops drastically and in long games where the terrain is full of craters and stuff the FPS can drop as low as 20-40 even when there's no action at all. And CoH 2 doesn't even raise my CPU or GPU temps above 60 so it's not even near full load for either one. Sounds like a bad optimization and / or a memory leak to me. I don't expect my rig to run it at 60-100 FPS all the time but the performance is way worse than it should be.
Would be interesting to hear other players' rigs and performances for comparison 
Well, I have the exact same thing, game starts -> 90-120 fps -> stuff happends and the 40 fps hits the field
For me CoH2 eats RAM slowly more and more, I've used up to 12GBs out of my 16 while streaming the game for 5-6 hours straight
As for your comparison games you mentioned, I'll give a few of my own: Fallout 4, ALL maxed, even AA 60+ fps all the time, BF4 Maxed with AA low, 60+ fps most of the time, if shit hits the fan with 6 tanks and Jets fighting then fps might drop to 40