Lower weight rated wd hitch on a heavier trailer, unsafe?

Good question. I believe and maybe wrong but having a lower rated wd you cause you not being able to shift all the weight, prabably some but not all. In other words lets say you need to shift weight of 200lbs but the lower rated wd would only shift 125lbs. This maybe acceptable, again I maybe wrong, providing you only needed to shift that 125lbs or less.