[kvb]

I like the way Scott Alexander frames the effect size. This is from the conclusion the blog post you link:

  An important point I want to start the conclusion section
  with: no matter what else you believe, antidepressants are 
  not literally ineffective. Even the most critical study – 
  Kirsch 2008 – finds antidepressants to outperform placebo 
  with p < .0001 significance. An equally important point: 
  everyone except those two Scandinavian guys with the long 
  names agree that, if you count the placebo effect, 
  antidepressants are extremely impressive. The difference 
  between a person who gets an antidepressant and a person 
  who gets no treatment at all is like night and day. The 
  debate takes place within the bounds set by those two 
  statements. Antidepressants give a very modest benefit 
  over placebo. Whether this benefit is so modest as to not 
  be worth talking about depends on what level of benefits 
  you consider so modest as to not be worth talking about. 
  If you are as depressed as the average person who 
  participates in studies of antidepressants, you can expect 
  an antidepressant to have an over-placebo-benefit with an 
  effect size of 0.3 to 0.5. That's the equivalent of a diet 
  pill that gives you an average weight loss of 9 to 14 
  pounds, or a growth hormone that makes you grow on average 
  0.8 to 1.4 inches.

Note that this is the over-placebo benefit, and placebos already have a large benefit in most depression studies.