Advisors who encourage their PhD students to take a leave if they are struggling with depression are being responsible - grad school can be a long hard slog and it isn’t for everyone. If your cohort felt they were in an unhealthy environment, in my opinion it was of their own doing and not because their advisors encouraged leaves.
We’ve had 2 PhD students commit suicide in the building in the last 15 years. We faculty are not trained in suicide prevention. The best we can do is encourage any PhD students who are struggling with depression to separate temporarily from the stress of graduate research and focus on managing their health issues.
When I had PhD students suffer from mental health issues, I encouraged them to step away and focus on health first. One student came back, found a way to manage the stress, and flourished. Another did not find a solution, decided to abandon research (left the program with a “consolation MS”), and found a different fulfilling career path. Both made the right decision, both are now happy: one is a tenured faculty member in another university and the other has a government regulatory position.
When our undergraduate students struggle due to mental health issues, we also typically advise them to take a leave. If they perform poorly enough, they are separated and forced to take a leave. It may appear punitive in the moment, but it is not intended to be - we are trying to encourage them to focus on health first.