First of all, the Dodo-Bird Effect is probably like the Flynn Effect: a statistical creation, not a reality, and definitely a "wet streets cause rain" causal inversion. Having therapy of any form is more likely to draw attention to problems, which is why "talk to somebody" and not "talk to a licensed psychotherapist" is said frequently on our streets.

QuotePost-hoc modeling showed the moderation was driven by faster rates-of-change for the mindfulness intervention relative to the others. In sum, we found that while psychotherapy modalities are similarly effective overall, some modalities are faster-acting than others.

https://link.springer.com/article/10.1007/s10879-025-09712-7

The DBE itself has odd literary origins:

QuoteHe referenced the Dodo bird's quote from Alice's Adventures in Wonderland, "Everybody has won, and all must have prizes," and his assertion that different therapies have equivalent outcomes became known as the Dodo bird verdict.

https://www.simplypsychology.org/news/dodo-bird-verdict