write their own papers on that topic As long as that topic is what they would like to research, I don't see a problem. And if it's not, then they chose a wrong

write their own papers on that topic As long as that topic is what they would like to research, I don't see a problem. And if it's not, then they chose a wrong lab/advisor. But this leaves them a very narrow set of skills I developed a pretty wide range of skills as a phd student. From developing device models in Spice, to Tensorflow. In fact, I wish I focused on a subset of those skills.