I tend to agree with this. The high end amps all clean up pretty nicely. There are exceptions. I owned an Engl SE once which did NOT clean up well in most of its channels. The second channel was not bad at it, but still not as good as most "boutique" amps or even low end NMV amps turned up to get some output distortion.Black face amps cleaning up poorly?
At Ultrasound we did a specific test with a Trainwreck Express, Komet 60 watt, Bogner Shiva, TwoRock Opal and E.Pro, Dumble overdrive special a Dr Z of some sort and Peavy Classic 50. We cranked the amps up, and dialed back on the guitars volume to see if the Trainwreck actually cleaned up as good as some people claim. What we found, was all the amps were extremely similar. What matters is the amount of gain that is dialed in, or the amp naturally has if its a Non MV amp. The amp with the least amount of gain, almost always cleaned up the nicest. There was no amp that did it better than any other. The guitar and pups make a bigger difference, especially in the amount of high end loss you achieve.