"On average." Except you must define the average. Temperature is the average energy level of a given mass.
The issue is we can't qualitatively measure the average temperature state of the CPU, only certain sections of it. So it cannot be proportional to power, since as you said, only instantaneous measurement of certain areas of the CPU.
We also can't easily define temperature as proportional to the power because the thermal transfer of different parts of the CPU conducts heat (power) at a different rate. The 14nm portions is not as dense and conduct heat away at a faster rate, and thus would read temperature differently.
Heat transfer rate between two masses increases as the difference in temperature increase. This means that as the CPU heats up, the heatsink becomes more effective as transferring the heat out. This means it is not proportional, as being proportional means it shows a linear relationship.
However, there will be innate thermodynamics interaction of the heatsink assembly as well. It may will a thermal saturation point where it becomes highly inefficient at transfer heat. Which also means, it is no longer proportional.
TL;DR: Unless the CPU and cooler are at constant equilibrium state, and that you are able to 100% measure the average temperature of the CPU mass, temp=/= power.