This is a pretty big assertion that the piece casually drops without backing. The reasoning as to why "chemical imbalance" is a bad descriptor is apparent* from the study [0] the author cites, but there is nothing that backs up this statement, which seems to be the crux of the whole piece.
*Even the study cited about placebo affects on depression doesn't _really_ prove the author's point that "chemical imbalance" is a bad term, it just proves that we do not yet understand the processes by which drugs treat depression. If we do not understand the processes, how can the author make the assertion that the characterization they are against is wrong? At most, they could claim "we don't know yet" but certainly not that "chemical imbalance" is categorically false.
[0]: https://www.frontiersin.org/articles/10.3389/fpsyt.2019.0040...