I'm a tenured professor of clinical psychology who doesn't focus on therapy in research, but who does focus on meta-analysis.

A. This either true or not true depending on how you look at it. There are standards of treatment, but the differential evidence in favor of any given treatment is usually poor except in some cases so it is difficult to justify any particular approach. There is no reason to mandate a specific treatment from a licensed professional if there's no strong evidence in favor of it over any other.

B. Licensing requirements are all over the place, but in some ways they are overly stringent. The licensing requirements per se aren't the problem, they're the admitting standards of certain programs, and the abuses of for-profit degree programs, which can actually be quite predatory. By the time a psychologist is licensed, the level of clinical training experience required by most states is probably equivalent to a psychiatrist. Many psychologists with bio backgrounds from reputable PhD programs (note many of these students do neuroscience or genetics research of some sort) have the odd experience at a particular point in their careers of being unlicensed but being more familiar with psychiatric issues (including drugs) than first or second-year psychiatry residents.

The meta-analysis in this piece is interesting, but not novel. Similar things have been shown in other meta-analyses in the past.

If you asked me to summarize the literature on therapy from a meta-analytic perspective, this is what I would say:

There is strong evidence that therapy is effective, from all sorts of randomized controlled designs with all sorts of controls (behavioral, pharmeceutical controls of all sorts).

There is little evidence of differential efficacy between therapies overall. This means that, e.g., there is no real evidence that CBT is more efficacious than psychodynamic therapy, despite what you might think or have been told. There is some evidence that for very specific targeted outcomes (e.g., reduction of a particular type of behavior), some therapies are better, but not for general outcomes.

There is evidence of publication bias. If you adjust for this, the positive effect of therapy does not go away, but it does reinforce the lack of differential efficacy. CBT and behavioral studies as a literature show the largest publication bias in previous second-order meta-analyses. (I want to point out that drug therapies also have problems with publication bias, as do all sorts of other scientific studies. This is a problem with science at the moment.)

The effect of individual therapist dwarfs that of therapy type. That is, there is strong evidence that there are very good therapists, but we don't really understand what they are doing.

There is some evidence that therapist-client match and cohesiveness, is important. So if you don't feel like things are working with your therapist, try a different approach. Incidentally, this is also true of drugs; trials show that people might fail with one drug but succeed with another.

I want to point out that treating (or hell, assessing and measuring) mental illness is a difficult problem, regardless of how you approach it. The ambiguities in the field are not because people are just stupid. There are very intelligent people who have been working on these things from many angles, and things are complicated and multilayered, from genes to social systems. Many good ideas just don't work, or don't work the way you'd think.