We as a faculty are responsible for the success of our colleagues. If we hire a new PhD, we need to guide them effectively to be ready for tenure review. And when a colleague is tenured we need to guide them effectively so that they are ready for promotion to full professor in a reasonable amount of time. Of course, they need not take our guidance, but they ought to know what is expected, and if they don't deliver ... At the same time, if our colleagues do not deliver, we cannot then promote them--even if they are wonderful and have become part of our community.
When we hire someone, presumably we have done enough due diligence to be quite sure they can deliver. If we are not quite sure, we cannot hire them. We have to have a sense, at that hiring time, that there is a sensible path in the next 2-3 years, at least.
Moreover, our expectations of performance must be in accord with what is possible. Some institutions provide much greater support and less demanding teaching loads than do others--and usually they are the strongest institutions. If if we want to be the peers of the strongest, we need to provide the same conditions. If we cannot afford that, then we need to have a good sense of what we might expect in terms of contribution.
And we have to have a review process, for promotion and tenure, that is demonstrably fair. If committee reports are unbalanced--too positive or too negative, given the evidence, we fail. If we keep being unable to tenure the junior faculty we hire, or promote to full our associate professors, what are we doing that makes that possible? If our candidates keep leaving for jobs at other institutions, are we doing what we need to do to retain them. That they leave after being denied a promotion, and end up in superior positions, is indicative.
The burden is surely on the candidate. But if we do not do our job, we ought be ashamed of ourselves.