The problem with heat is it takes time to generate. While this is taking place, you are losing transient energy and decay in your music. These products do well to show you an improvement, but they also come at some serious costs to the energy of the music. Sometimes you don't realize this until you pull the absorptive product out of the system. I've done this with two clients recently who used isolation/absorption products under their components. After removing the products, there was an energy to the music again. The clients listed those products for sale the next day.
The key thing here isn‘t heat generation or time. Its vibrational energy levels. Ideally vibration is conducted out of a component via a low impedance interface (good match in density and stiffness) into an increasing compliant medium. The heat conversion is therefore remote to the component. Any loss of musical performance in the component isn’t caused by the heat conversion process, which happens outside of the component, but rather by the presence of vibration, which as mentioned above becomes locked into the component should the isolation/absorption product form a high impedance interface with the component across which internal vibration doesn’t pass. The result is that the internally generated vibrational energy is locked within the component instead of being lead away and converted to heat. This is the reason isolation products give the results you’ve noted.