The article has an interesting argument structure. First it undermines the science behind psychiatric drugs by referring to their discovery as serendipitous. Then it proceeds to point out that there is no good theoretical understanding for how the drugs work, even if there is understanding in what neurotransmitter levels are effective. Then the author proceeds to drop the "not better than placebo" results.

Without knowing any psychiatric science, this narrative nevertheless seems suspicious. First of all, it is entirely irrelevant whether a discovery was made serendipitously or as a result of incremental science, as long as the effect is clear enough to be repeatedly found. This is not true in well understood fields, such as physics, where the theories are mostly not changed every now and then, but in complex fields, such as medicine and social sciences, the fact that something matches pre-existing theory is no evidence per se. The problem is "bumpy" enough that any theory is likely to flatten every bump that is not directly observed, even if that bump would be very useful in practice. This leads to most discoveries of any value being serendipitous. It also leads to incremental research failing to advance rapidly most of the time.

So the lack of theory and serendipitous discovery are not problems in themselves. The finding that psychiatric drugs would not be better than placebos is indeed a problem. It does raise the question, of how the serendipitous discovery was ever made. Did it arise out of spurious correlations, so that when the drug was first discovered there happened to be a big incidental recovery in most treated patients? Then in later retrials people managed to trigger a sufficient placebo effect to get the whole thing going. It does seem a little unlikely, but one would have to examine how the first trials were performed.