Does this mean psychology is useless? I don't think so, there have been many people helped by application of psychology, but the sooner we take it out of the same category as for example mathematics or medicine the sooner we can move on. I'd love to be convinced otherwise that we as humanity have a chance of understanding ourselves to the point where we can draw meaningful conclusions about human happiness or other feelings/states of mind. However, I think at this stage our chance of accomplishing this is similar to a medieval blacksmith doing a successful root canal treatment on of his dental patients.
I'm definitely looking at the advancements in AI with hope that perhaps replicating our own thought processes in machines will enable us to study them more systematically and to understand them, but these are still early days.