While this comes to the right conclusion I think it mistraces a lot of the issues. For example: a fair amount of the depression and neurogenesis studies (and indeed neurogenesis manipulation studies) suffered from the same issue: it's really hard to make a population of cells die without generally poisioning the remaining cells. Most of the initial studies relied on things like radiation, ie radiate a rat and it starts acting depressed. There is now increasing evidence that radiation kills off a bunch of synapses and causes some wicked disregualtion across the system so that turned out to be wrong. Conversely BDNF enhances neurogenesis but it also enhances synaptic learning so even positive manipulations had this issue but in reverse. Newer timed genetic manipulation studies were more precise but the depression-neurogenesis link has been slowly losing steam in light of these studies.

But the BIG issue boils down to this: there was never strong evidence for the importance of neurogenesis. The dentate gyrus is a tiny region of the brain with neurons that act in unusual ways. In humans it's an even tinier region. While it is probably required, at least as a pass through, to learn new memories, it's surprising how much weight people were placing on neurogenesis in this tiny tiny structure. Given, networks can make small zones have big effects, but the weight of evidence should have always been on people pushing the area to prove the dentate was this massively important structure. This has not been conclusively done (studies have linked it to some specific subtypes of learning but those have limited it as much as they have found an important role for it). This is a structural issue in science broadly, there is an incentive to push forward with the next big finding but no incentive to go back and confirm the gulf of assumptions that a literature is resting on.

The good news is, human brains could always change, synaptic plasticity is present throughout life and has been shown by many good studies to occur throughout adulthood. We don't need new cells in a tiny part of the brain to learn new things, networks rewire and while that rewiring isn't something as dramatic as new cells, small effects can lead to big outcomes in dynamic systems. People obviously make new habits, learn new skills, and make new memories throughout life. The onus should have always been on science to show why it occurs, not to lend credibility that it occurs.