Why are people using the full setting? Games for the X1 are developed for limited, and movies and tv-shows use limited as well. If you use the limited setting (it's called TV on the X1 I think? At work now, so can't check), you will get a correct range. It's probably due to the name right? "Limited" sounds like it's worse than "Full", but it really isn't.
I have never seen a TV that can't display the limited (16-235) color range, but I've seen a lot of TVs that can't display the full (0-255) color range. The issue seems to be the worst for people that use incompatible settings (i.e. full on the X1, limited on the TV or similar), and it seems the best when both X1 and TV are set to use the limited color range.
If you experience black crush, try the limited color range and reconfigure your TV and see if it's still there. If you're using a PC monitor to play on, then I don't know since they are usually created for the full color range.