Power handling isn't subjective but it is not exactly meaningful.
Meaningful information would allow you to pick an appropriate amplifier and assure safety margins. Power ratings don't do that. The popular thermal test doesn't give users information that allow them to make good choices. If anything, it gives people a false sense of security thinking that as long as they don't have an amplifier that can exceed the power rating the device is safe from thermal damage.
That isn't correct and it isn't correct for ANY transducer. There are more variables at play that determine how much power your subwoofer can handle. The big ones are the type of signal used, and the frequency it is used at. It helps to understand that the primary way heat is dissipated from the woofer is from air movement over the coil. In resonant systems the woofer almost comes to a standstill at the tuning frequency of the port or PR. If you pump a test signal into the driver at this resonance point you can toast the driver WELL before you reach the power rating.
The Audioholics article on this is good. It comes to the same conclusion that I have. The power ratings are almost meaningless numbers and if anything, they cause more harm than anything because people don't understand the situation and unknowingly overdrive their subs.