The game all of a sudden started struggling with a very noticeable slowdown ... cpu utilization is only about 30% max
If the framerate is dropping with only modest CPU usage, that suggests it's bottlenecked on rendering in the GPU hardware. That's a hardware limitation, rather than being anything to do with the software, so even switching to a different tool won't help if your game does the same thing with the GPU. Lots of people blame us for every problem they have even if it's nothing to do with us...