When you finish the campaign there is a chance that you'll get a box with random items/rarity but it doesn't give mythic there is no chance to it..
So that makes it useless anyway.. So i think removing the boxes in campaign loots would be much better in my opinion.. I rather earn SM currency than earning boxes with useless items, The only way to make it worth it is maybe adding chance of earning a mythic item to it.. After the "Major Update" i didn't really feel that MAJOR changes in the game.. Only UI recustomize layouts/backgrounds.. actually I'm disappointed that it takes several hours long to update a 15MB sized update that doesn't really much improved anything in the game :/

The boxes are better. A box will give you more power (the only useful thing you can get for SM credits) than the SM credits would have given.

This^
Common sense if u think about it.