Aren't we conflating two things here?
The study in the OP is saying the theory behind anti-depressants is incorrect and even fabricated: that is, the "chemical imbalance" idea. That doesn't mean that medication affecting serotonin levels won't help with the "feeling".
If someone says they are feeling down, we could prescribe heroin. Suddenly the depressed person feels "better". We could even hypothesize that depression is cause by "low opioid levels". We would say, "see, when they get their opioid levels up, things are better."
For a drug to be used to "cure" something there has to be a proven cause/diagnosis of the problem first.