I think the top 8 schools for MBA programmes are not the same as the best schools for PhDs, and the best schools are not always the largest schools. Also, I don't think that the volume of research being generated is a primary indicator of MBA quality; that will always be salary.
If you look at this chart:
https://twitter.com/DuncanChapple/status/545982932503232512/photo/1 you'll see that the 13th, 14th, and 15th schools in terms of the volume of 4* research, the highest quality, are Oxford, Cambridge and Edinburgh. It would be ridiculous to suggest that such a ranking means that those schools are very poor: they are much, much smaller schools than the ones above them. Edinburgh has fewer than 100 academic staff: it is half the size of Loughborough Business School, for example, yet produces more 4* research. Obviously the volume of research that small schools produce is modest; the quality of the research is a better guide to the quality of their PhD programmes.
I'm at Edinburgh for many reasons. it's a research-centred school with a tiny and highly selective doctoral programme. It is the only business school in the world where there is a group of academics doing work on my research question. It's an ancient and beautiful university. Endowed in 1583, the wonders of compound interest and Scottish thrift make it Britain's third-richest university. The resulting resources (both human and material) are unimaginably better than I hoped. It is (unlike larger triple-crown schools like London Business School, Lancaster, Cass, Warwick and Manchester) deeply integrated into a broader university, and that is important for my research: I am a psychologist, supervised by professors in different departments (Indeed, in different schools: technology studies, in social science; and innovation, in the business school). I can thus be part of an interdisciplinary research cluster based in Europe's largest centre for informatics research. Another example: Much of my research focusses on the documents of life and, this semester, I am in a doctoral seminar developing exactly the tools needed for that with researchers from the Edinburgh Law School, from the schools of sociology, psychology, and education, colleagues from the business school, and our new Centre for Narrative & Auto/Biographical Studies. I don't think I can have that high-quality and interdisciplinary experience in English anywhere else outside the USA.
Above all else, of course, I am at Edinburgh because they want me. The business school admitted me, and put me forward for a scholarship. At my age, that is remarkable. There is no way that, for example, London Business School or City University would have admitted me to their PhD in management, even though I hold masters degrees from those schools. Even at Edinburgh, there were 500 applicants for 20 PhD places. I am lucky to be here.