Quality is somewhat subjective but I have a pretty good nose and taste buds and my buds have never smelled or tasted better under COBs. I also had several comments from people I share with after I switched, many asking what the "new strains" were (same strains/phenos grown under different lighting). Quality and terps were great under the 315's but definitely a step up from that with 3590's ime.
Not a tech snob and will likely use my 315's again if the situation calls for them. But I'd definitely stop short of saying quality is better under 315's and I used them for 2+ years. I've yet to see anyone say "I should have stuck with hps or CMH" after switching over to COBs.
BTW: I define quality in the context of smell, visual and taste. Not how high the THC is, THC is one of 70+ cannabinoids and only one factor in how high you get.