There was a % to get a specific item of “X” tier according to u having this item already in inventory.
Next time u got a fortune box for example, u landed an epic, then the item u get is likely to be the one u dont have yet. Same with legendaries. If quantity of different items in you inventory is equal then system work as usual.
I think that way player can experiment more with builds, get certain items for specific builds in late game.