A point I think is crucial to mention is that “effect size” is just standardized mean difference.

If a minority of patients benefit hugely and most get no benefit, then you get a modest effect size.

This is probably why this discussion always has a lot of people saying “yeah, it didn’t help me at all” and a few saying “it changed my life.”

I believe we should be focusing on more relevant statistical methods for assessing this hypothesis formally. Basically, using mean differences is GIGO if you assume you’re comparing a bimodal or highly skewed distribution to a bell curve.