Maybe we can administratively limit the number of years people spend doing science, in the same way as the presidents are limited to at most two successive terms in office.
We pretty much do already. How much science does the typical University scientist do as their career progresses? As in so many fields, people get promoted out of their field of competence and into management.
It's the only absolutely reliable way of getting rid of bad leaders.
This might not be a good enough reason to oppose longevity tech, but I don't think it's easily disposed of.