An engineering manager having 5-6 direct reports would spend the same amount of time in a company. I guess PhD students would be mentored by postdocs, the same way juniors are mentored by senior developers in the industry.
Those direct reports aren't (nominally) trainees though. Part of the "deal" is that you're being underpaid because you're being trained.
Mentoring by more senior folks in the lab certainly helps everyone (https://www.pnas.org/content/116/42/20910), but it's barely measured or rewarded for PIs and not at all for postdocs. Changing this would be an easy fix though--ask for a reference from a junior colleague when hiring.
More generally, there's a huge disconnect and sudden between the skills needed to get a faculty job (i.e., publishing a high profile papers as an individual contributor) and the skills needed to do well at it (e.g., management). Everyone is all antsy to shorten postdocs, but I'd actually be in favor of making the career path more gradual with so people get some mentored management experience.
Mentoring by more senior folks in the lab certainly helps everyone (https://www.pnas.org/content/116/42/20910), but it's barely measured or rewarded for PIs and not at all for postdocs. Changing this would be an easy fix though--ask for a reference from a junior colleague when hiring.
More generally, there's a huge disconnect and sudden between the skills needed to get a faculty job (i.e., publishing a high profile papers as an individual contributor) and the skills needed to do well at it (e.g., management). Everyone is all antsy to shorten postdocs, but I'd actually be in favor of making the career path more gradual with so people get some mentored management experience.