Absolutely they work. The don't require a commitment from uke to fall so much as a commitment to attack. I always viewed kokyu throws as the unbalancing part of the kihon waza done large enough that nothing further is needed. The implication of which being that if you don't get uke's balance with the kokyu enough to make them fall it should just flow into another waza.
If you cannot do a kokyunage, you cannot survive against stronger faster and more flexible opponents. Then you are just doing Jujutsu with the aikido syllabus.
curious as to what you mean by that?