Fifty years ago if you had a problem you would run to the head of your department as she/he knew all. Industry and government agencies used to wheel them in when there was a problem; but not now. Specialization rules now, since fruits from low hanging branches have been harvested, and one needs to stretch farther and go further. It is more often than not the research assistant knows about her /his subject than his professor. The question is who you would send to the classroom to teach.
In most places, older professors are teaching first-year students and the younger ones teaching the advanced undergraduate/graduate courses; which is right as the older professor has more experience to make things comprehensible to young students.
In the past teaching, the university courses carried a lot of prestige since there were not too many who could teach. But know universities looking for their staff to bring money, thus research has taken over. In the UK students are expected to pay £10,000 tuition fees annually. With this fee comes the demand that what they are getting for their money, which means teaching is important. However, students choose their university according to their rank in the league table which is disproportionately influenced by publications and research funds.
My question is this
Teaching or research is supreme at the university level and why.