One problem is that being a PI no longer seems to mean what it used to. For a PI, productivity is writing grants and getting other smart people to do research and write papers. While it may vary from field to field, I've worked for several PIs who have fantastic funding and are great at marketing their research, but don't have the knowledge to reproduce their own labs' experiments. My impression is that, for many successful scientists, the career arc goes something like:

- Get really good at doing science as a graduate student and postdoc.

- Become a junior PI, spend most of your time selling your science, and train your graduate students and postdocs for a few years. You need to keep up with the literature to know what to do next, but you rarely have time to perform experiments yourself.

- Become a senior PI. Now your lab is established, and you can hire half a dozen knowledgeable postdocs to teach the others in your lab. As your field advances, you need to keep up enough to sell the discoveries your lab has made to grant review panels, but you don't actually have to know how to do the science. That's for those below you.

There are some clear exceptions. Some PIs really do know how to do everything. Some PIs even keep running experiments while also writing grants and running a lab, although that's not necessarily an easy task. But for most PIs, the arc above seems to be the way it goes. You take the brightest, most talented scientists, and once they reach they become really knowledgeable, you turn them into professional grantwriters.

I'm not sure what the solution is, but I feel like there has to be a better way. To start, maybe we should think about limiting lab size, so that your lab seeks to maximize the productivity per employed scientist rather than the total amount of funding that you can obtain. Without so much pressure to accumulate funds to grow their labs, perhaps PIs could spend less time writing grants and more time running labs. Also, with smaller labs you can afford to hire more PIs and give a career path to more of the postdocs that you are "training."