8 cores, 16 threads, CPU doesn't even break into a sweat. Same with GPU.... yet frames are still not hitting 60.
Something being bottlenecked in Odyssey because it doesn't utilize the full performance of the system.
If your GPU isn't hitting full utilization, then it's a CPU or related (possibly memory) bottleneck. Doesn't need to be using all cores for the main game loop or a render thread to be starved for CPU time on one core, and most apps that measure CPU utilization don't poll fast enough to catch all spikes.
The game has become better at utilizing more threads, but it hasn't become less dependent on a few key threads. I doubt they did anything to the renderer at all, probably just got better at offloading other stuff (like AI) to separate workers. You still need a few very fast cores, in addition to sufficient aggregate CPU performance.
You have a Ryzen 7 Pro 2700 don't you? This CPU has plenty of aggregate performance, but it's a Zen+ architecture that tops out at 4.1GHz.
My Zen 3 part holds ~4.7GHz in Odyssey and has, conservatively, 30% greater gaming performance per-clock. Aside from transient loading pauses, I can hold over 60 fps in the most CPU limited EDO scenarios I can find, but not by a huge margin. There is no practical way for this to be possible on any Zen+ part without a non-trivial performance patch that does more than just grasp at low-hanging fruit.