The comment about a robotic approach to teaching circuits is interesting. When doing my wobbly prop conversion some months after getting my PPL, my instructor told me to stop flying "numpty PPL stude circuits" and tried to get me to approach the circuit as an exercise in progressive energy management (starting from when you join or level off from the climb out). Doing it this way, the power setting can often be a lot lower a lot earlier, but I can appreciate that in aircraft with little power to spare it may be thought best to keep the power a bit higher.
If people are following slower aircraft but still religiously flying all the numbers they were taught, they may end up over extending and enlarging the circuit, rather than slowing down and keeping tight by, eg a power reduction and even a stage of flap early on.
To this it might be said that you shouldn't be encouraging students or low hours PPLs to fly slowly at 1000 feet or lower, but I'm not talking about dangerously critical airspeeds or angles of dangle, and being able to chug along at (say) 80 knots instead of 95 ought to be something the average PPL could handle as a result of his/her training.
Of course none of this takes account of the loony circuits imposed by noise constraints. Quick straw poll of how many GA airfields have circuits which are "standard" on all or main runways? North Weald? Duxford? What others?