Adding some more personal experience to this thread (statistically, as useful as a chocolate teapot, of course).
I am very (most would say far over-)qualified for my job as a state primary school teacher in a school with an...interesting...mixed intake. First class Oxbridge degree, PhD, PGCE,management experience in industry etc etc.
I almost never use the content of my 'subject' degrees in class teaching (although, enquiring 7-8 year olds being what they are, I dip into it when answering individual questions on a surprisingly regular basis).
I use the skills my 'subject' degree and PhD taught me - rapid assimilation of new information, synthesis of different sources of information into a coherent whole etc - a lot. Planning a topic or a block of lessons is very similar to planning an essay in many ways.
During my PhD, I tutored undergraduates, and that did give me some experience of direct 'knowledge transmission', imparting information in a structured way to bright children.
It is my PGCE which taught me how to teach, and in particular, how to teach children who may not be disruptive, may never waste time in a lesson or require superior 'classroom management' skills but do find it hard to learn, ie for whom straight 'knowledge transmission' teaching is never going to work.
It seems to me that a false dichotomy is being set up in this thread between 'teaching bright children in a selective school, who need lots of 'lesson content'' on the one hand and 'teaching children in other schools, where the main job is classroom management'.
Where I teach, classroom management is a doddle. Behaviour is excellent. What is a huge challenge is teaching classes with a spread of abilities spanning 6 years or more (in a single year group) and ensuring that all the children make progress. I find teaching the (extremely) bright children in my class easy - they learn as I do, and I find my own education useful in understanding how to challenge them. Where I expend huge quantities of thought and intellectual energy and teaching skill is in understanding what it is my lower ability and SEN children do not understand, what their barriers to learning might be, and how to accelerate their progress. The knowledge I need to do that comes from the training I received during my PGCE - at the university but more particularly through coaching and mentoring during teaching practice - but the 'intellectual capacity' which led to me gaining the qualifications I got in the first place comes in handy when juggling lots of competing information about lots of different things in order to plan the best way forward.