In my opinion, St Andrews University is actually an amazing university to study undergrad in. I've now experienced a larger university and i'll be perfectly honest and say i can definitely see why St Andrews student satisfaction is so high. I've never gotten a better education than at St Andrews. In terms of teaching and admin, St Andrews is actually second to none. The only thing I would improve is the amount of information about competitions and start ups etc, I feel St Andrews can be a bit isolated when it comes to conferences etc.
When it comes down to it, there is definitely a correlation between larger undergraduate student bodies and lower student satisfaction. Money and funding can alleviate some of that, as you can see with Oxbridge but as a whole it seems to follow this curve. The way I theorize it is that if you had 5,000 students and 5 admin vs 50,000 students and 50 admin, the ratio of admin to students is the same but it is so much easier for 5 admin to work as a team than for 50 admin to work as a team. When you work in a team of 50, its harder to make team decisions and harder to get things done, its also easier for one person to slack off and not do their jobs properly and sort of hide under the team umbrella.
About research, there are soo many prestigious universities in the US that don't do much research. In fact, Americans don't even look at world rankings just because they are so often based on research and not actually selectivity and student satisfaction that they are not useful. For example, schools like UCSB and UC Boulder do amazing in research based rankings but in reality they are just state schools with huge student bodies that basically cater mainly to your average state student, while schools like Brown, Dartmouth, Rice etc are top schools at teaching and highly selective but don't do research but definitely provide a better student experience.
IMO, St Andrews is the closest thing the UK has to a Brown or a Dartmouth. They share many similarities, being smaller universities with a strong arts faculty with a long history. We can all say St Andrews are Oxbridge rejects, but the truth is a Brown student is probably a Harvard reject, but at the same time that Brown student probably rejected a huge number of top universities to go to Brown and is very likely to be hired by a top firm no different from that Harvard student if of the same capabilities.