I dont think its a myth its more like the guys said before about build quaility and honestly preference, power, and current draw.. I currently have 7 or 8 amps in my possession and have owned many many many more... I am in the middle of a build and decided to have a head to head with my Arc Audio xxk 4150 (badass specs for a decent price), Monitor 1 2.70 (cheap price great build quality), Zapco c2k 2.0 (possibly SQ myth amp), and last but not least old school zapco z250c4...
I played each one of the amplifiers on tweeters, mids, midbass.. They all were different and I would use different amps for different reasons..
Honestly for midrange and tweeters I would rank the amps
1. C2k 2.0 2. Monitor1 3.z250c4 4.xxk4150
Midbass was totally different BTW all amps were bridged
1.xxk4150 2. C2k 2.0 3. Monitor1 4. z250c4
I ranked them based on my needs and personal taste. I honestly think that the Zapco c2k amplifiers are the BEST bang for buck SQ amps... They beat the pants out of most high end amplifiers IMO in price, power, and sound.. I have had arc SE, TRU, Helix etc... There is no comparison.. Honestly in my test I was pulling for the Monitor1 because of price and Size, Thinking I could sell the rest and get more than 60 bucks an amp, but in some test they just didnt match up totally..
So bottom line High END amps are NOT a MYTH depending on the amp and what your needs and taste are..