I would like to know more about this because I am suspecting a CPU bottleneck in my case, but I am not an expert. I have an old i7 4820k (from 2013) + 24GB DDR3 RAM + RTX 2070 Super. So far I have had 0 problems running any game at 4k60FPS, including Battlefield V or the last Call of Duty. I played Horizon smoothly and without any performance issue, but with Odyssey, I am experiencing the same awful performance as many others here. I can't even think of getting close to a planetary basement.
No matter the settings, I don't get even 30 stable FPS on foot whether I play full low or full ultra. According to MSI Afterburner, GPU load is 50% ish, CPU load the same, so perhaps no bottleneck? Do you suspect that I might be having a CPU issue? It's disheartening because the expansion looks promising but right now is just money wasted.
You may very well be CPU limited with a 3.7-3.9GHz Sandy Bridge-E part, especially if any given logical core is near full reported utilization. However, this should not be assumed, despite low GPU utilization.
The most straightforward way to see if there is actually a CPU bottleneck is to manipulate the CPU speed and see how much performance changes. This should be easy to do with an unlocked 4820K. Just go into your motherboard's BIOS setup, reduce the CPU multiplier by 5x (knock it down to 32x for 3.2GHz or so) and then run the game again in a similar scenario and see what the frame rate is. If it's a proportional reduction, you were predominantly CPU limited. If not, you're probably GPU limited, even though the GPU isn't fully utilized...it's stalling on something and more CPU performance probably won't help.
A very repeatable test (the suit tutorial) and monitoring software capable of logging frametimes (MSI After or NVIDIA FrameView, for example) will help a lot, though if the difference is large enough (unlikely) you can just eyeball the in game frame rate gauge.
Also, make sure you've done the basic performance diagnostic stuff...complete reset of in-game graphics settings, any driver profiles for the game, cleared shader cache, etc, and rebooted the system, just to rule out potential configuration issues that could skew results.