Yeah it’s an oft-quoted line. And then again there’s plenty who say that good speakers and/or Harbeths can do any genre. There used to be a poster on the Naim forum who championed Spendor 3/2 models as the supreme rock speakers.
I think at least some of it has to do with snobbery. Real music is civilised, whereas morons who like rock just want boom and tizz, that kind of thing. People who know very little about the music in question opining on behalf of others in a way which shows their prejudice more than illuminates the matter, basically. And not helping that prejudice, there’s a post by Alan Shaw somewhere saying that to make a rock & pop speaker he’d have to do things differently, essentially beefing up max volume, boom and tizz.
I think that’s completely wrong, at least for the properly heavy end of metal. There’s loads of poorly produced, harsh sounding albums where the last thing you want is any extra treble emphasis. And many producers already use tricks to get the sound they’re after, eg toppy/clicky kicks, so the recording already has what it needs without speakers sticking their oar in.
Personally I prefer the equipment to be able to deliver things like a guitar sound with guts - one thing that piqued my interest with Harbeths was hearing Dismember on P3s. Loads of (‘modern’) hifi seems to de-emphasise the low mids in an attempt to sound transparent or detailed, and it kills metal IMO. If anything I’d like these 30.1s to be more warm/gutsy, not less. They’re really good though, and even if some day I try Classic 2/3s or something like that, I think I’ll be keeping the Harbeths for some time.
Other reasonably proper metal I think works well as a test are the first track on Heartwork (palpable quality to the guitars) and Under A Serpent Sun off Slaughter of The Soul (can sound toppy sometimes, needs to sound gutsy).
Today I’ve mostly been on a bizarre nostalgia trip through the soundtrack to the original TMNT film from 1990 though, so I’m not a reliable witness!