Yes, theoretically good therapy could exist that theoretically could help some people, but this is about CBT/DBT. And YSK the largest CBT study ever showed it had no benefits:

PsychologyToday.com:

At six-month follow-up, patients who received CBT were no better than those in the control group... One hundred percent of the patients were clinically depressed after completing treatment.

"Selling bad therapy to trauma victims" @ psychologytoday.com

And Cambridge said there's no long-term benefits:

Cambridge.edu:

Counselling is associated with modest improvement in short-term outcome compared with usual general practitioner care, and thus may be a useful addition to mental health services in primary care.

https://www.cambridge.org/core/journals/psychological-medicine/article/the-clinical-effectiveness-of-counselling-in-primary-care-a-systematic-review-and-meta-analysis/4F4EC30F86DDB334BBF257A091AAFC6E#

Similarly, a psychiatry professor fact-checked claims (made by the APA) that therapy works:

Psychiatry professor Jon Shedler:

Let’s fact-check this by seeing how it aligns with the findings of the largest and arguably best randomized controlled trial behind the guidelines.
The RCT was funded by the U.S. Department of Veterans Affairs and the Department of Defense and published in the Journal of the American Medical Association.[6]...
Patients received [either] - a “highly recommended” form of CBT (prolonged exposure therapy) or a placebo treatment.
Here is what the study found:
Nearly 40 percent of patients who started CBT dropped out. They voted with their feet about its value.
Sixty percent of the patients still had PTSD after completing treatment.
One hundred percent of the patients were clinically depressed after completing treatment.
At six-month follow-up, patients who received CBT were no better than those in the control group.
Nineteen serious “adverse events” (suicide attempts, psychiatric hospitalizations) occurred over the course of the study...
I did not choose this study as an example because it is a poor study. I chose it because it is arguably the best.

https://www.psychologytoday.com/us/blog/psychologically-minded/201711/selling-bad-therapy-trauma-victims

For clarity, the author isn't saying good therapy can't exist, or doesn't exist. He believes insurers don't want to pay for quality long-term therapy, so they fund cheap forms of therapy that don't work and customers quit the therapy. (Which saves insurance companies money.)

He also believes that good therapy (if you can find it) takes months to show benefits.

             Study: Therapists are in denial.  

The BPS (British Psychological Society) recommends therapists actually listen to clients, eg asking whether they like a particular therapy or not.

Why why don't therapists ask this? It's because many therapists don't even listen to clients:

Clinicians generally react with resistance to client feedback systems. Lambert quips: ‘‘If you think you’re a superior clinician, as all clinicians do, then why would you feel you need it? Why collect data that can only bring you down?’’

https://www.psychologytoday.com/us/blog/psychologically-minded/201711/selling-bad-therapy-trauma-victims

While the BPS recommends recording patient feedback and changing forms of therapy based on it:

The principle is simple – before each session, ask clients a few brief questions about how they are feeling and how they feel the course of therapy is going. These days, it can even be done on a palmtop at reception while they are waiting to see their therapist. By comparing a client’s answers to the average progress made by similar clients at that stage – that is, clients who had similar problems, of similar severity, at treatment outset – Lambert’s algorithms are able to say whether a client is ‘on track’ or ‘off track’.

https://thepsychologist.bps.org.uk/volume-21/edition-1/when-therapy-causes-harm#

             Harm of therapy.  

The BPS explained how many therapists are totally unaware of the harm clients report from therapy:

Brown University Medical School surveyed 181 practising psychologists across America, they found that a significant portion (28 per cent) were unaware of negative effects in psychotherapy.

https://thepsychologist.bps.org.uk/volume-21/edition-1/when-therapy-causes-harm#

             The form of therapy is irrelevant.  

Studies show what really matters is who is doing the therapy (ie their social skills) and not the form of therapy.

eg:

• "Lambert’s work is that it has tended to reveal that outcomes have more to do with the therapist than with the treatment approach they use"

https://thepsychologist.bps.org.uk/volume-21/edition-1/when-therapy-causes-harm#

             Clarification.  

Therapy should be a great thing for some people. But really:

• There are many people who can not be helped by any amount of words because they have real life problems that aren't going away.
• Many clients do not want blame-based therapy that assumes the individual is defective.
• Many clients don't want to relive trauma.