There is also a sense of tautological definition here. "Linear" isn't well defined, and seems to be being defined in terms of the goal. In the strict meaning (y =ax + b) no amplifier is linear, ever. The universe can't hold such a device. All amplifiers have bandwidth limits, and in addition to being a natural consequence of existing, any properly designed amplifier will impose a bandwidth limit in order to ensure stability.
Power delivery is a slippery problem. No amplifier used for audio purposes needs to deliver its rated power continuously across the audio spectrum. All that does is require that the amplifier be able to fry tweeters. OTOH, the instantaneous power delivery does need to be there. But only for milliseconds. The power spectrum of the humble triangle is something to behold.
Modern switching topology amplifiers need more care in imposing requirements, as simple naive metrics that were satisfied trivially as a consequence of the design of conventional amplifiers may become hard, and yet for the purposes of actual audible results useless. Within in a fixed budget (and they all are) a requirement for flat power delivery across the aubible spectrum may well be detrimental to the performance of the final product, as it will be in competition with other goals, goals that have an audible impact.
