I've seen both psychologists and people who were just therapists (typically with a master degree in social work.) A psychologist has a doctorate in psychology, a PhD in psychology. That higher level of training makes a clinical psychologist (the type who do treatment) competent to come up with diagnoses.

The main goal of therapy is to help the patient learn to better cope with the stresses of living. Having a PhD. degree doesn't make a psychologist necessarily any better at doing that than a social worker. The main person who has to deal with your problems is you, not the professional. No degree makes anyone more expert at dealing with human problems than anyone else. Experience successfully helping people is important. But there is really no way of knowing how good anyone is at that based on some credential. You really have to just work with the person and see if it helps you.

My own extensive experience with therapy has made me realize that no therapist ever solves your problems, no matter how many degrees the therapist has. That's pretty much on you, but checking in with someone who knows your life story can help keep you honest about whether you are really working in a direction that is productive.

I have found that both types of professional counselors, both the psychologists and the ordinary therapists, tend to spend the time they meet with you chatting about whatever happens to be on your mind when you walk through the door. In my experience, that's not real productive, other than to make you feel listened to for a while.

Therapy can serve to educate you about disorders of the mind. In that, a psychologist may be most capable. But getting educated about your disorder doesn't naturally translate into getting a better grip on dealing with your problems. Some people accumulate all kinds of knowledge about psychology, without managing to improve their lives very much, if at all.

If knowledge about the mind gave you a good life, then psychologists would tend to have the best lives. They don't. I once worked taking care of the children of parents who were both child psychologists. I didn't stay long in the job because these were two of the most obnoxious, ill-behaved children I'ld ever met. They were bad enough with me and even worse, when their parents were in the house. So knowledge about the mind doesn't not predict skill in coping with life. That takes wisdom. There is no special degree that tells you how much wisdom a person has.