The root of psychology is godless humanism. It cannot be Christianized any more than the alter of Satan can. It claims to answer questions and solve problems that only Scripture holds answers to.
Yes, it is a usurper, and has no place in Christian life.
That’s a wrong generality too. Science is a neutral thing; it is the study of empiricisms. It is the use to which the knowledge thereby gained is put, that is either evil or good.