Dependence on pain compliance is the lowest form of martial arts technique. As long as you continue to practice this way your partners will always be falling due to the need to escape pain (or the anticipation of pain), preventing you from advancing to higher level technique, where control is achieved by taking your partner's center...kuzushi, on contact, leaving your partner bemused as to how their balance is being broken - as they are not feeling any obvious compulsion (pain) to do so.
The pain caused by nikyo in particular can be easily cancelled out by someone who possesses a certain set of body skills, usually resulting in uke getting kuzushi on nage
. Also there are quite a few people where nikyo causes little pain at all, either due to "nerve damage" or other anatomical differences. I know a wrestler who was completely impervious to the pain of the nikyo pin. The guy's wrists were probably the same size as my hands. Depending on pain compliance to control a guy like that? No way, not on this Earth..