kung lao's probably the best non-ninja human fighter in the MK series barring lui kang. that puts him somewhere right equals or slightly below the younger version of shang tsung in mk II and III...
I would say kung lao's far deadlier and possibly even more skilled, but lui's got his power level going for him which is just naturaly higher than kung's...
motaro... meh, I'd say he's probably above youthful shang tsung or equals with him, but definitely below goro, or kintaro...
he's actually one of the weaker bosses, the only reason he is a boss is because the shotokan (goro's race) lost their two strongest warriors...
he's pretty equal (just slightly above) with shiva who's nothing more than a personal body guard and lacks any seriously dangerous power IMO.