Well since a common thing therapists do is (covert) social skills training, increased extroversion makes perfect sense. The was recently another one linked here that said long term therapy can increase neuroticism.
My biggest complaint is that most of their studies suffer from survivor bias. They ignore people who drop out or have negative outcomes (there is overlap there).
My biggest complaint is studies being inadequately placebo-controlled. It's not just that studies often have no control group or a blatantly different control condition (waitlist, pill placebo), it's that there's no consensus on how psychotherapy works. That means there's no agreed-upon approach for sham psychotherapy, and even assertions that it's impossible to do because virtually any therapy-like experience already contains most of the beneficial elements (cf. [1]).
My biggest complaint is that most of their studies suffer from survivor bias. They ignore people who drop out or have negative outcomes (there is overlap there).