Premium unlocks some stuff it looks like also a 10% bonus exp, a house, and some other slight advantages.

Obviously premium has to be beneficial or else the game would go broke, but it doesnt seem like its too superior.

Have you ever try Entropia Universe? It's 'free to play' technically but you use real money as currency in the game, its pretty challenging, there are people who have never deposited money on it, and now have characters worth over $10,000 USD. It's one of my favorate free to play games because of it