Actually, are you sure a meta analysis isn’t a primary source? Having worked on one in the past, you’re often having to reanalyze data and the finished product is quite unique. Even “structured literature reviews” I think count as primary sources, since the author adds to the literature their own perspective and they are generally peer reviewed. That said, when you cite things professionally, you will often have hundreds of sources. Most researchers, legal scholars, etc., just keep a database of their citations for easy callback. It’s important because at the upper levels, different authors might speak of the same objective findings in two different ways and with two different frameworks, so the aggregate loses that. It’s not something non-professionals necessarily need to care about, but you do want to train undergraduates on that proper methods so they’re ready if and when they go to graduate school.