Re: On who should teach beginners
If everyone that turned up stayed (like in the koryu school ideal) its an easy answer - the most senior or near most senior teacher as tradition suggest
But in the modern world where 1 in 10 might still be training in a months time, its a sure fire way to burn out the best instructor through (pearls of wisdom before swine?) and deprive the senior students (esp. if there are limited classes) of what they need to develop (and the interaction that helps the instructor develop). Maybe this deprives the dojo of looking after existing customers at the expense of recruiting new ones.
from a time management point of view if a black belt student is 1 in 500 (and most stats seem to indicate that they are) then spending an hour with them is like spending 500hrs with beginners, with only limited hours for aikido (or anything) in a week it might be the best investment of time
The flip side to this reasoning is that all the research in skill acquisition shows that early experiences are the most powerful and thus when the senior instructor teaches beginners it might be the best way to 'light the fire' of excellence. And anecdotally looking back at the videos of many of us rank and file aikidoka you see that after that short spurt of learning at the beginning, many people move essentially the same way that they did back when they started.
well enough ranting from me and enjoying the discourse