The framework for this statement is wrong. In the UK, where teaching doesn't matter, research rules, and all universities are research universities, the preference ranking might go from something like 'stars' to 'middle-range academics' to itinerant lecturers; but for many US academics a teaching-heavy position at a SLAC is preferable to research stardom. In other words, while it's true that most 'stars' are concentrated at research universities, it's not true that there's necessarily a quality dropoff (or even much of a research output dropoff) after the 'stars.' At my SLAC (selective, but not Amherst or Williams) most of the faculty had top PhDs and were also top researchers, hardly 'middle-range academics.' I don't doubt that they could have (sometimes did, when they left) competed for jobs at Stanford. And many of them came from top research jobs previously. And many of them preferred the SLAC model and environment, and, at least ostensibly, enjoyed and/or valued teaching. This is something I don't think most British students and academics I meet really understand--that the hierarchy of success among the US professoriate isn't solely determined by one's research output.
If you are saying that many of the professors at SLACs in the US had the potential to be top researchers at R1s but chose a different career track then that is certainly true. And there are definitely people doing good research at SLACs, but overall the people doing most of the research most valued by disciplinary peers are at R1 universities (at least in STEM and "harder" social sciences). So they are not "top researchers", though they could have chosen that track.
Does everyone in the British system aspire to be a "top researcher" and feel like they have failed if they don't get there? Maybe it's true to a greater degree than in the US but I doubt it is generally true. There are teaching oriented universities and research oriented universities just like in the US. The same applies here in Australia (which I am more familiar with than the UK). And teaching performance definitely counts here even at the top research universities though research is weighted more strongly at Go8 universities. At the next rank in research terms (UTS, Macquarie, Griffith, Wollongong, RMIT) teaching and research are ranked about equal (I was told the 40,40,20 split at interview - at my current Go8 institution it varies by department). Though there are people doing reseach at places like University of Canberra, nobody thinks that they are "research universities".
