gtx 1070 armor, i5 6600k 3.50 Ghz 16gb ram etc
NORMAL LAG
A quick look at your specs makes it seem you have plenty to play the game. It may not be butter smooth late game because the CPU load gets heavier as the game progresses. There are more units that need to have vision, pathing, etc calculated every frame of video. Units will also bunch up more blocking pathing and producing even more calculations. Every pixel of the game is drawn more as damage textures are splatted onto the already densely drawn terrain etc.
GPU
Your GPU seems to have 8GB or RAM which is plenty for COH2. Setting to larger textures than your GPU can hold internally will drastically reduce your FPS. A friend once said that reducing the physics settings can help FPS a lot. I would start there GPU-wise. Perhaps there is an issue with nVidia physics or the driver.
CPU
Is there a chance your CPU is not actually running at 3.5 GHZ? CPUs normally clock down when nothing is happening to save power. I have heard people have issues with certain Motherboards where the CPU is clocked way down all the time. Usually a setting in the bios. Alt-Tab to windows and check the frequency or use a program such as CPUID HARDWARE MONITOR which will show you all the cores and their freqs and temps.