I think you're under estimating just how hard it is to prove that an anti-depressant works. The placebo effect is massive. The tools to measure depression are more qualitative than quantitative. That's why a number of pharma companies have abandoned neuroscience entirely.

Yes, you only need 2 positive phase 3 trials to get your drug approved. Yes, you could have done 10 others and had them fail. Yes, the FDA already knows this.

The FDA is willing to approve drugs for depression with much weaker data than say, cancer, because if they held them to the same standard, no drugs would be approved at all.