My personal preference is a variety of artistic styles to reflect the spectrum of games and gamers. This is one of the reasons I've been turned off by the "iconics" in 3.x era and Pathfinder. I don't like the look of a unified campaign world "look" in a core book (though in a campaign setting book, that's fine). Depict steampunk dwarves on one page, Hyperborean barbarians on the next, traditional epic fantasy later, some gothic horror, and so on. Art should be inspirational to players and appeal to a broad spectrum. I think this is best achieved by displaying many types of campaigns in a variety of settings, rather than one standard.The way I look at it, as a game system, it should present itself in a relatively neutral manner that can fit in most settings. The setting is what should suggest social, gender and economic realities. If someone wants to make a setting ala Conan where women wear bikini mails and are cattle for muscular conquerors, so be it; some people grew up reading that stuff and will take interest in it. But the game system itself should be really open and allow for a large variety of settings.
The 5e PHB does this better than 3.x or 4e.