I really like LoL's pay model. The main source of player power in the game is in the form of Masteries, which all players must play to unlock. Everything else it the game (minus skins) can be earned after playing for a while. While you can technically "buy" power (runes that give your champions permanent buffs), that same power can be earned by players who've earned enough in-game currency, buying with real money only gets you it faster. Champions are the same way, where any player can unlock them with in-game currency, however, players that can purchase those champions with real money to unlock them faster.