Let's get something out of the way. There is absolutely no way to objectively review music. But even more than that, there is no way to quantify talent. Publications, like this one, crop together Top 10 lists on any number of subjects. But all those lists are really doing is listing the preferences of the writers themselves. There is nothing wrong with that, but it will always be a point of contention.
With that out of the way, the argument (or discussion) inevitably turns to a "Band X is better because Y," a practice that goes nowhere fast. And, unfortunately, that usually descends into the utter nadir of all music debate; the notion that somehow records sales can be substituted for band quality. That thought has become to go-to statistic for fans of all music, including our beloved metal, to justify their most personal opinions. It's as if people have to prove that the band that they like is measurably better than yours, and how many records they sold, digital downloads they have, or preorders they got is the evidence.
I'll take care of the easiest part first. Without using his name, for fear of this entire blog collapsing under the weight, a certain Canadian pop star sold 137,000 copies of his debut EP. This was before his name became synonymous with cookie cutter pop music. In comparison, Norwegian progressive black metal band Enslaved, an established band with some twenty years under their belts, sold a mere 2,300 copies of "RIITIIR," a masterpiece in it's own right in the first week of US sales. How many people, outside of the Beliebers themselves, would say that that settles the quality debate? If you are in the business of catering to the masses (read that as little girls), you are certain to see the numbers swing in your favor.
The second part of this is slightly harder to explain. It is the expectation. If you were to get in touch with the heads of Nuclear Blast, none of them would say they expect the new Wintersun album to dominate the American Billboard charts. They aren't looking at the possibility of selling 500,000 copies. This isn't to say they wouldn't LOVE it, but it just isn't practical. And you know what? They seem perfectly content with that. Metal labels, in general, seem to have better practices when it comes to controlling costs, maximizing profit (an entirely different rant all together), and maintain a better relationship with their talent. They aren't trying to force the next big thing down your throat, which shows as much respect for the fans as it does for the bands themselves. Poor sales, particularly in North America, aren't going to doom you to being cut and relegated to the pits of obscurity forever.
I admit that this argument is, itself, a subjective one. But before you turn to those weighty numbers to settle your friendly debates, remember this: Unless you are in the upper echelon of artists that have sold more than 300 million records to date (a list that includes the Beatles, Queen, and Michael Jackson), there are plenty of bands, singers and rappers that have sold more albums than your favorite artist. But you wouldn't admit that Madonna is better than Rush... would you?