Hedonism states that happiness (in whatever form one chooses to interpret it as) should be the highest good and ultimate goal in life.

But happiness is a rather weak emotion, it is easily crushed by other negative emotions. Meaning is the highest good and ultimate goal of life, happiness may come as a result, but suffering may also. You can take somebody's happiness quite easily, but it is difficult to rob somebody of their sense of meaning. I find it quite evident in human nature that meaning is the true goal, and happiness is more of a distraction. If happiness were the best goal, movie stars and multimillionaire entertainers would be the poster children of mental health with every luxury they could want, instead they end their own lives at staggering rates, most likely because becoming a marionette on the strings of public opinion does not offer much of a sense of meaning. We long for purpose, and that longing has shaped human history, one might argue that it has been the source of much suffering, and yes it has, but we are here. We did not collapse into savagery, Human civilization exists because we seek a sense of meaning. Not because we seek instant gratification and temporary pleasure.