This happened to me, but i got passed it but the hall of heroes is when it starts to feel like when you have to pay physical cash for the transmutation of energy.
As you know the crafting for a 3 star item is 2k crown plus 200 CE. getting CE is not easy.
I know you can convert your crowns into 100 CE at a price around 8k crowns.
And its not easy getting crowns.
To get crowns you need to do missions. But the elevator is very expensive too as well with a price of 10 mist per pass.
This might be very troubling to a lot of players. I haven't had this problem because i bought an antigua and a sealed sword. Also i purchased in game cash with physical money.
Something as far as Rank 5-2, I think that should be changed considering this game is free to play.
My humble suggestion. I got passed this mission already myself, but I heard a lot of complaints about progression to the other missions
Four and five star suff will be even more painful. Try repeating boss missions a lot: they usually pay out better.
Also, to craft stuff that needs 200 energy, you only need to use 100 ce and 100 mist.
Remember, the devs intentionally want you to pay. So patience is the key.
But you definitely need some 3*gear. This game can get pretty hard.