Though, lets remind ourselves that the power to fly the "normal" circuit, could in many cases be about cruise power - which does not really afford the engine much opportunity to begin to gently cool down.
Cruise power in my 172 is 23/2300 which gives 128kts. Circuit power is 15/2300 which allows me to get into the 85kt white arc for the second stage of flap. There is no way that I can fly a circuit at anywhere near cruise power and still get the speed back enough to get the flap in and land.
Maybe in some aircraft you need cruise power to fly an airliner circuit to a massive runway but to fly a normal circuit then you are a very long way from cruise power and thus a very long way from shock cooling when making power changes.
I have yet to fly any variant of 172 that required cruise power to fly a normal circuit.
I fail to understand how a glide after circuit power is going to shock cool. As explained the circuit power in a 172 is very low, the engine has already cooled during the circuit, taking the power off is not going to see much more of a change and certainly not enough to shock cool.