Happiness is one feeling among many that we should experience throughout our life. I think happiness is a byproduct of living a fulfilling life. To do things we feel are useful is definitely important.
Are they the most important to me. No, not at all. I think feeling that I have lived life with a lot of great experiences with other people is the most important.
Some of those experiences are useful ones, some are just being in the moment, some are both.
If you talk with elder people, they will typically say that the things that mattered throughout their lives were the experiences they had with other people.
There are many experiences that add to a life well lived and they are different from person to person. For me being in nature, reading a book alone, being active with people, doing sports in nature, exercising, building startups, being with my wife or daughter, etc. etc.
Are all these experiences directly useful to other people. Not necessarily, but they are still very important to feel alive and live life.
Obviously during your day it feels great to work on something that has a bigger purpose than just enjoying ourselves. And I think it is important to have one or more things in our daily life that we can put our energy into and that we feel are very useful to other people and our environment. Should it be everything we do? Not at all.