No, really. Anyone using TSMC nodes seems to get hotspots with their end products. My entire current machine is a case study in that phenomenon. Also die size and positioning matters. Some manufacturers (*cough*AMD*cough*) make cooling more "interesting" by positioning heat sources in very specific parts of the package. It can, at the very least, change where you want to position your TIM during the mount. It can make HDT coolers worse since some of the pipes might not line up well with generally-hot areas of the IHS. Etc.
Just because something is good at cooling a 13900k doesn't mean it's good for cooling everything else.
It's been a few years since Heat Transfer in college... but here goes, let's discuss.
There is of course validity in what you are saying. As you know there are 3 types of heat transfer, conduction, convection, and radiation. Heat is transferred from the CPU to the cooler contact plate via conduction. Assuming a high conduction material such as copper and good contact between the surfaces there will be limit to the heat transfer coefficient between these two surfaces.
Next the heat must be removed from the system. With both air and water eventually air is used to disperse the thermal energy from cooler.
The greater the temperature difference between the cooler contact plate to the CPU the greater the heat transfer. And a cooler that can dissipate more thermal energy will maximize this difference thus maximizing heat transfer. Hot spots or no hot spots thermally a more efficient cooler will work better on both a homogeneous and heterogeneous hot silicon.
Assuming the contact between the cooler and CPU is optimal I assert that a cooler that can move more joules will be better on both an evenly heated CPU and one that has hot spots as the heat moving in the cooler will immediately "flow" to the cooler spots, thus the ability of the cooler to dissipate heat will ultimately be the limiting factor on it's effectiveness. Again this assumes optimum heat transfer from the CPU to the cooler in both cases.
Now I will admit there are many other factors to be involved here. If you take a cooler that can move a lot of heat on a CPU that is evenly heated but has shitty thermal contact to the CPU that's going to be a bigger problem than a CPU that can't move a lot of heat but has great thermal contact. This condition would be better for a CPU like Zen 4, which has hot spots yet doesn't need to remove as much heat as the 13900K.
But in reality most high end coolers have very good thermal contact and are made of materials with high thermal conductivity so as I wrote above when dealing with real world examples where thermal contact to the CPU is optimal the 13900K based on it's thermal demands is a great test unit for CPU cooling.
For this not to be the case we'd have to be talking about a theoretical niche case on the far end of the spectrum of what actually happens. ie find a cooler that can handle the 13900K but can't handle the 7950X both operating at max manufacturer specs? Won't happen. But I bet you can find a cooler that will handle the 7950X but not the 13900K. Hot spots are much less important than overall cooling capacity. If you have pick a CPU to test on I stand by my assertion that the 13900K is a great one.