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".
Other ideas for making bank include-
1.) Charge 10x as much for trinket/weapon slots + only give one weapon slot free
2.) Shield slot must be unlocked for 500 ce per month
3.) Worse odds in prize boxes, but don't tell people, just put "<1%" and lower it
4.) Don't let players craft chaos! Sell it to them in one of the above "<1%" boxes.
5.) Non-reskin weapons should deal less damage than reskins of weapons.
6.) Rolling UVs should cost energy instead of crowns and should also be more expensive.
7.) No free battle sprite at the start of the game. Players who received them should have theirs revoked.
8.) Auction house should be unlocked for 1000 CE before players are allowed to use it.
9.) Players should only be allowed to trade if they've made a purchase at some point.
10.) Player-Player trading should have a fee associated with it.
11.) Knight color should cost 50K cr per month to maintain, whereby your knight fades to gray otherwise.
You might think this would make players angry. That's both perfectly fine, and can be avoided by introducing changes slowly. You don't remove the radiants all at once, instead you decrease the drop rates with each prize box update until they still drop but at 1/10th what they do now. You don't just revoke the sprites or chaos sets, you do so but with compensation. UV tickets can make up for any misunderstanding.
Make Radiant Fire Crystals buy-able by trading in Tails Tails
Radiant Fire Crystals should also be able to be bought by trading in Level-10 5* equipment