Normal people are born with two legs. If someone unfortunately has only one leg at birth, they will compare themselves to others and feel great pain. But if normal people were born with only one leg, then no one would feel pain.
So having one leg or two legs is not important; what matters is whether you have what most people have.
The feeling of "happiness" arises through evolution. Unhappiness drives us to take actions to improve our situation and increase our chances of survival, but it can also lead to depression and reduce survival probability.
Comparing yourself to others can affect your sense of happiness; I think this should be considered being "enslaved by the brain's instincts."
I feel happy about the existence of my consciousness. Where did consciousness come from? It comes from the brain; the brain arose during human evolution. Humans and other animals can be traced back to single-celled organisms. How did cells arise on Earth? How was the Earth formed? That leads back to how the universe was created. What is outside the universe? Is our universe simulated?