So it's interesting. Looking at the meta-analyses more closely than I have in the past raises more questions about ACT than I thought based on the way it's discussed in the literature. However, in general, the pattern is that it shows efficacy relative to controls but not greater than other treatments (although this is a common pattern in the psychotherapy literature that applies to almost every type of treatment):

https://www.karger.com/Article/Abstract/365764

https://www.sciencedirect.com/science/article/pii/S016503271...

https://www.sciencedirect.com/science/article/pii/S000579671...