There is much more to a PhD than research output. The unwritten curriculum of a PhD program is to introduce the student to the field of research through apprent

There is much more to a PhD than research output. The unwritten curriculum of a PhD program is to introduce the student to the field of research through apprenticeship. For example, you hear people talk more about who your dissertation advisor was than what your dissertation was about. Writing a dissertation requires more than just "brains". It's about building relationships with professors that serve on the committee, learning how to manage feedback, and navigate the other aspects of academic life. If publications is all it matters, universities would just give out degrees based on published papers alone but few institutions do (at least in the US. I don't know how it works in the EU). As you point out, sometimes enrolling in a PhD gives you access to a well-equipped lab that is necessary to do the work. Most research in the physical sciences requires that kind of set up. I am in the social sciences so it's not a lab science. I could have written the papers I am writing in my garage but I don't think that the experience would have been the same as being a PhD student. By the way, at least in the US, there are a lot of research staff that works on research projects and publishes without having completed a PhD program. They probably have more knowledge than some PhD in the same field.