Leibniz did publish one huge book, the Theodicy, and edited a number of other sizeable volumes which collected together documents he had transcribed from unpublished manuscripts held all across Europe. So a request for double-weighting would likely have been met with little resistance.
But of course the Ref is not all about the number and quality of outputs. How would Leibniz have fared on the other criteria – impact, and contribution to his research environment?
Pretty well for both, as is happens. Sure, he failed at the time to find an impactful use for some of his research, such as his discovery of binary arithmetic, which eventually had a huge impact when used as the basis for modern computing more than 250 years later.
But even allowing for this, the impact narratives that Leibniz could have written over the course of his career would still have been mightily impressive. After all, he rewrote the legal code for Mainz; built the first fully functional calculating machine that could do addition, subtraction, multiplication and division; advised high-ranking officials and royalty on matters of public policy; and established the Berlin Society of Sciences.
It is much trickier to assess Leibniz’s contribution to his research environment, as there wasn’t really a research environment that he could contribute to. After all, he never held an academic post, and instead spent most of his life as a court counsellor and librarian in the relatively small German town of Hanover, often complaining that there were few people there he could speak to about his scholarly pursuits.
This non-academic career path also meant that Leibniz did not supervise any PhD students to completion or undertake any external examining. He did, however, have an impressive record of grant capture, inasmuch as he was often successful in getting his employer to provide financial backing for his research projects, such as his scheme to build windmills to drain the silver mines of the Harz mountains (which cost 2270 thalers, a sum almost four times Leibniz’s annual salary at the time), and a two-year trip to visit a number of historical archives across Europe.
Ultimately, then, we can say that Leibniz probably would have thrived if the Ref had existed in his day, and in fact would have been a Ref superstar. But the irony, of course, is that he (and all of the other great philosophers) managed to achieve all that he did without the incentive provided by the Ref.