Get rid of all the RNG stuff. Just have a store where you can buy items.

For example:

T-Rex Mount 1000
Red Mage Barding 1000
Wind up Mithra 250
Anemos Jacket 100

Have more things appear as you level. Like the T-Rex mount doesn't show up until you hit lvl 17.

Maybe put some really high priced stuff that shows up when you hit lvl 20, like Scorpion Harness 2500 loot boxes or something.

But this turning the boxes in and then having to clean out crap from your inventory every time has to go. At least give me the option to say whether I want the item or not. Then if I say no it doesn't go into my inventory.

Just a couple of ideas. Loot box turn ins are really the only that I truly dislike about Eureka.