There are real differences in expectations between universities, even without factoring in non curricular undergraduate research. At some schools the intro geology class is just a series of short essays or even multiple choice questions. At others, the intro geology class demands that students be able to write 10 page field reports, do basic analysis (qualitative and quantitative), and research in depth on a particular topic.
Name two top schools which rely on non professors, or other non obviously qualified individuals, to lecture. There’s a huge difference between Gen. Petraeus lecturing about Iraq War policy and a harried grad student doing the same. In fact, by almost all metrics, it’s the less elite schools which make the heaviest use of adjunct labor in teaching undergraduates.