CX is not singletrack, courses are most typically wide enough that a stronger racer can pass a slower rider along majority of the course without resorting to cutting them off. Even if you are racing against a well match competetor, there is ample opportunity to let you legs do the talking, not your hips and elbows. Also consider that a smart racing move often will be to let another racer lead, so you can get some draft on the faster sections and conserve a bit of energy.
If you are getting lapped, you definitly should back off momentarily and yield the good line when getting overtaken.