The game is not multi-core/thread optimized at all. The whole game runs almost completely on only one core.
Most games do so. I'm not at all surprised. To me, this behaviour is the normal case.
To me, you are acting as if you demand that pretty normal streets should be replaced by Formular 1 racing courses ...
That's just not true. I've written about that on my last post:
Unreal Engine 3/4 -> multicore optimized
Frostbyte Engine -> multicore optimized
CryEngine -> multicore optimized
Anvil/Ubisoft engines -> multicore optimized
Unity -> multicore optimized (if you want so)
And you want to tell me that "most games" do not use multiple cores? The engines mentioned above cover about at least 80% of all big PC games. Of course some small 2D indie games don't use them but often they also don't need them because they don't offer spectacular graphics that makes multicore optimization important.
But D:OS is no small indie game with crappy graphics. It's a big game with a modern engine which requires quite some hardware. That's the big difference...
It's strange that the engine uses 3 or 4 cores while using an i7 and one one or two cores when using a Xeon. They should use exactly the same since they are basically the same tech/CPU...
