If players can't farm radiant fire crystals at all they'll just give in and hand over their wallet to buy energy to trade for them. Then, by increasing the prices they will have to pay more, increasing your revenue even further. Think about it like this-
When a game presents you with a paywall of some sort, do you...
A) Uninstall the game? Of course not. There are no other options for games. Not even a choice. No real dilemma.
B) Pay upwards of a thousand dollars a month, so as to have the fine privilege of "the best" gear that functions better than "that other gear".