MacBooks have terrible thermals. They will thermal throttle before most laptops, much less even compared to a desktop.
Also, laptops generally have CPUs that pull 15 watts. Whereas desktops have CPUs that can pull 95 watts or higher (sometimes up to 150). The difference is astounding.
The 15/16" MBPs have a 45W CPU TDP; they can run CPU continuously at at least 45W as long as your ambient temperature is normal-ish and the airflow isn't obstructed, and can do 60W+ if thermals are cooperative.
