This is a discussion that has bothered me for a long time. There are debates and studies which try to suggest that one or another of "first to file" (FTF) or "first to invent" (FTI) is better for one or another type of inventor (small inventors, etc).
A recent article in IP Osgoode demonstrates the problem. In referencing a study the article suggests, "The study finds that the shift to FTF resulted in a reduction in the number of patents granted to individual Canadian inventors and small businesses". This is a study based on the Canadian experience having made the switch to FTF in 1989, with the USA switch coming into force in 2013.
The assumption of the article, and most of the debaters, is that if some patents are good, more are better. The fact that the number of patents granted went down after a change should not be presumed to be a bad thing, when in fact patents not being granted may just as easily be a good thing for innovation.