IMHO, you need both the leverage and some of the pain for yonkyo. Relying on pain alone can be tricky since it may or may not work. It's good that you learned the leverage "version" first. Learning to coordinate your legs, hips, arms and upper body when applying the leverage is essential.
I've studied under senseis that taught both and I found that by doing the leverage movement with some pain to act as a distraction / extra motivation for uke, you get consistent results.