What that standard is asking, is not a real word scenario.
First of all there is no such thing as running an amplifier at 150W for 5 minutes when playing audio.
It is also extremely unlikely that a person would play anything through any amp that would even peak at 150W, as your ears would not be able to handle that.
A very realistic scenario is audio that peaks in the 10 to 25W range. This is where BOSC will have the best performance.
If all amplifiers are specified based only on that standard it would actually not tell consumers how the amplifier performs at levels that they will be using it.
It doesn't matter whether you like, or agree with, the established standard. Lobby the FTC to change the rule if you think it is flawed in any way. Otherwise, advertise your products in accordance with the various ratings requirements if you are selling those products into markets where such adherence is mandatory (pretty much all countries AFAIK). It's very straightforward, and hundreds of respected manufacturers have been doing so for 45+ years.
Manufacturers have tried in the past to water down the amplifier rule and apart from some very minor concessions, the FTC has left the standard as it is. There is good reason for that- it keeps manufacturers honest and ensures customers get what they paid for.
It seems you want the perceived legitimacy of using an industry standards based AP analyzer, but aren't prepared to specify the amplifier according to the industry standard required for advertsing power and THD. Can you see the irony?