I think most people would agree with that statement, if you ask them to think about it a little more. Happiness, or "expected happiness" is just one term in the utility function. There is also "expected unhappiness" which might encompass things like suffering, pain, negative emotions. The concept of utility tries generalize enough to add these things together, but at an everyday conceptual level these seem to be different things (nevermind about how emotions manifest physically.) For instance, we can be happy about one thing and yet about another e.g. "my infant daughter is beautiful, but I'm sad that my parents did not live long to share this joy with us." People seem to understand this: in English we have the word "bittersweet", and the juxtaposition of joy and melancholy seems to be present in many other languages and cultures.

Back to the question of value: are people more eager to avoid loss than to pursue potential gains (of the same order of magnitude?) Experience points to most people putting more effort into keeping what they have, even if they are relatively unhappy with their situation. Part of this is probably evolved defaults of the brain influencing even what you might call conscious decision making.

And don't forget about morality. Although we might try to reconcile the two, there is often some tension between doing what is "right" and doing what we expect may make us happier.