A related note from Apple:Apple could design a cooling system for the 2018 Mini which allows all six i7 or i5 cores to run at their full Turbo speeds at, say, 80°C. That's a simple engineering task, but of course that would result in a much larger case to house the much larger cooling unit. Apple is under no obligation to do that, much like Dell is under no obligation to do the same in their tiny Optiplex 7060 USFF units.
In my opinion, the takeaway here is that recent Intel design changes have enabled significantly higher maximum clock speeds when in Turbo mode and also allow more power usage than the CPU is rated for. While you will see those benefits in shorter-term jobs, you will not see nearly as much with longer jobs in the typical smaller chassis computers, which are in vogue nowadays. Performance running at stock non-turbo speeds is unaffected by this and continues to work as advertised.
Apple Support said:If kernel_task is using a large percentage of your Mac CPU
Activity Monitor might show that a system process named kernel_task is using a large percentage of your CPU, and during this time you might notice more fan activity.
One of the functions of kernel_task is to help manage CPU temperature by making the CPU less available to processes that are using it intensely. In other words, kernel_task responds to conditions that cause your CPU to become too hot, even if your Mac doesn't feel hot to you. It does not itself cause those conditions. When the CPU temperature decreases, kernel_task automatically reduces its activity.