Not necessarily. I'm still measuring the same way today as I did in the 1970's and every product I have designed uses power based on RMS metrics and states THD. For MI applications, especially where the distortion harmonics components may be integrated into the signal in both the preamp and power amp, I have standardized on 10% because after a lot of test player contributed their perceptions, 10% was pretty much the sweet spot where most players liked both the tone and texture. The most common numbers I see for bass amps range from about 5% to 20%, depending on the application. For guitar amps intended to be overdriven as part of their native tone, 10% to 30% is more common. Of course, the amps must be tested and safety certified under these conditions if being honest.
For pro audio, the numbers are different of course, and as powers increase the duty cycle factors into the equation. This is most common at very high powered pro audio amps, where after a second or two, the limiting algorithms fold the power back to about 1/2 the rated power and in big powered speakers, the HPF may shift upwards and the crossover points may also shift along with the limiting thresholds. This was all started with Meyer, Renkus Heinz, Apogee and later with JBL, etc. This has allowed maximum performance with minimum damage and warranty claims.