Power rating standards promote transparency by curbing exaggerated claims, such as emphasizing high outputs during short 20 ms bursts or any other metric used to suggest "making the music louder." -Does it actually make my music louder?
It is really just a rating.
Companies can publish any ratings they like alongside the FTC rating, including their preferred "music power" ratings if they choose. Remember PMPO?
The key point here is that if all manufacturers use this one measurement (the FTC rating), it allows for straightforward comparisons among them, similar to how SINAD works. Does it give you all the information you need for your specific use case? Not necessarily, but it does serve as a performance indicator, much like the SINAD value.
If you need or want to, you can always dive into the spec sheet for more details, which may reveal metrics that are better suited for your specific needs.
IMO.