I also notice the following performance behavour: When I start e.g. a local Multiplayer game against bots, at first the GPU utilization is ~99% but when more and more units join the match, the framerate drops and utilization of the GPU drops as well. The CPU utilization does not change much.
I think the game engine is rather old and cannot scale on CPU Cores. So at some point the engine cannot feed the GPU with enough input. Even on high spec gaming rigs. I have both a system with a 5900x & RX6800xt & 32GB Ram and a system with 7800x3d & 4080Super & 32GB Ram and the behavour is similar on both.
That beeing said their are some tutorials on youtube on how to optimize the PC for this game that will give some gradual improvemt like putting the system on performance mode in windows (Energy Setting) etc
Just google "performance problems call to arms gates of hell".