This is an indictment of musical royalty -- people at the top who didn't earn their position and don't deserve it -- by a rebellious group of newcomers who are unburdened by false idols and who feel that their values are better and more pure. "We're better than you; we don't care about all this stuff that doesn't matter."
Having said this, the song is filled with jealousy and insecurity. Lorde resents the status, privilege, and trappings of success that the royals have achieved. You can feel this in the transitions to "But ever song's..." and "But everybody's like Cristal..."; these transitions don't make logical sense (what is the point that precedes and justifies the "but"'s?) and sound like someone complaining about someone that they are jealous of and can't stop thinking about.
The great irony of the lyrics is that "we'll never be royals" but she keeps talking about becoming Queen and talks about "ruling."
So on the surface, this sounds like a revolutionary group that wants to overthrow the current power, but who is subject to the same temptations and corruptions. Will Lorde's new rule be any better than the current regime? Who knows.
So in summary, this feels to me like competitive jealousy, rationalized as moralistic judgment and a comparison of values.