I see your point, but I wouldn't define RMS and Dynamic power like that.
RMS It is the continuous (long term) sine wave power that can be dissipated by the voice coil/magnet assembly without failure.
Dynamic watts is the amount of wattage that can be used for very short-term peaks in music. It cannot be used on a continuous basis. On a typical loudspeaker playing at medium loudness with an 88db sensitivity, if you were sitting about 10 feet away from the speakers an had an SPL Meter you might see a reading of anywhere from 80-85 db's. For loud you might get from 90-95 or so db's. Let's say while listening there is a sudden burst in sound (like in the 1812 Overture) that causes the speaker to pull enough wattage to momentarily play a 105-110 db sound. This would be the dynamic sound difference.
Obviously, the amp will draw more volts to accomplish a dynamic high, which will come from the alternator in a car, but this happens with home audio too.
Every movie and all music have a dynamic range, which will not be continuous. That's why I prefer RMS...it's a better measurement. And yes, any amp with 500w RMS is a good amp with clean/powerful sound.