It's a difference between worldly and spiritual happiness. With the pleasure that comes from the worldly dhammas, we're talking about sense desire or sense pleasure. This type of sense pleasure depends on Vedana - pleasant Vedana, which is impermanent and arises and passes very quickly. This type of sense pleasure is also dependent on things that we sometimes do not have the power to control. Even though it is pleasurable, it is impermanent and it cannot be depended on for our lasting happiness. There's the birth of pleasure and there's the death of pleasure. There's the birth of praise and there's the death of praise. Sometimes we get fame and we like it, and sometimes we get fame and we don't like it. So the worldly dhammas within themselves aren't really happiness; it depends on our perception of them. This is the difference between worldly happiness, the worldly dhammas, and Joy as a factor of enlightenment.
Joy as a factor of enlightenment is concerned with spiritual happiness that arises dependent on our inner beneficial mind development which, hopefully, we have more control over and is not so dependent on the pleasantness or the unpleasantness of the contact from the senses. It also has the capacity to last longer. Sometimes we have a pleasant feeling arising from the tongue, but unless we eat all day, which would turn into Dukkha, it doesn't last that long. However, if we're developing the unselfish emotions, the capacity to extend the power of these throughout our day increases as we develop. This spiritual happiness coming from our beneficial mind development and especially from the Joy factor of enlightenment has to do with confidence. How long we can experience this happiness depends on how long we can keep Mara and doubt at bay.
We also have the capacity to renew the spiritual happiness arising from the unselfish emotions within ourselves, which, in my eyes, makes this type of happiness superior. This understanding of how the unselfish emotions, and not sense desire, are the source of happiness, enables us to develop the spiritual and emotional maturity that allows us to let go of our craving for the sense pleasures on deeper levels. Without developing spiritual happiness, it's very difficult to let go of worldly happiness because we don't have any experience of something better. It's like someone going up to a little six-year-old riding a tricycle and just taking it away. Of course, the little six-year-old will get upset. But if we give the little six-year-old a two-wheel bike with the appropriate training wheels and teach the little six-year-old how to ride, then they see that it is superior to the tricycle. They can go more places, especially as they learn to ride and take off these training wheels. Then they can go very far.
Regarding pleasure as the ending of Dukkha; pleasure and pain in themselves are not the source of Dukkha; it's our reaction to them. So I wouldn't actually define the ending of Dukkha as the fading away of the worldly dhamma of pain. I would say the ending of Dukkha is more our wise reaction to either pleasure or pain, and letting go of our attachment to the body that experiences it.