Remember that you don't really need Radiant Crystals. All your 5* stuff works fine without 'em. Getting to level 10 is just icing on the cake. SO if you cannot heat up your 5* stuff, don't worry. It's not as bad as not being able to get 4* Crystals, which you need to progress.
I'm making this thread because in another place where I posted this realization, I got ignored...
Or you can just hunt boxes in "Alone in the Dark" and "FSC" on elite millions of times over and over and over again.