But The cpu is going to 90%+ would normally be 20% on my pc and maybe 40% on phones so....
Sounds like the game is CPU-bound so you should take a look in the debug profiler back in C2 and see what the busiest areas are. You can also run it on Edge on Windows and see how that compares.
IIRC the latest Edge update does improve JS performance a lot, but I'm not sure if that update has made it to the Xbox One yet.