The ability to take pleasure in one’s life is a skill and is a kind of intelligence. So intelligence is a hard thing to evaluate and it manifests itself in so many different ways. I do think the ability to know how to live a life and not be miserable is a sign of that.
Optimism is not inherently a superior way of viewing the world. Certainly doctors will say it might be better for one’s physical health to be an optimist. But, morally speaking it may not be appropriate in certain circumstances.