This talk of currency is meaningless because the digital content in these games, like baseball cards, has no inherent value. Instead, the value is determined primarily by supply, i.e. rarity. As the items become more plentiful, they lose their value. This is illustrated most clearly in games like Girls Kingdom where the primary difference in rarities was simply how hard they were to get, as the stats were very similar. Yet still, players strove quite hard to get these rare characters simply because they were rare.
In short, rare characters are valuable because they're rare. If they become common, they're no longer valuable. The talk of "greed" over Gatcha rates is misdirected (or not properly elucidated) because players will always want that which they don't have--and if they didn't, that would signal the game's imminent collapse.
A discussion that makes more sense would be where the game falls on the "pay to win scale", as you could certainly argue that design decisions disadvantage free players to a greater or lesser extent from game to game. How much of an advantage does a player get for $15/month? Is that advantage greatly increased for $100/month? Does the game reward money invested on a diminishing returns scale, or does return increase with each additional dollar (very insidious--players beware!). Is there an optimal breakpoint that gives you the greatest return for your dollar?