my third and last balance suggestion. Deck packs.
As simple as it seems, you should be able to pick a deck with certain trait (like you know dragon, shapeshifter, yordle, etc.) before the carousel start, it shouldnt grant you a certain champion, it would be ridiculous, but that would highly increase the chances for you to get more some of those champions in your last slot. So you would be able to have more sonsitency and not reroll 100 times to get the last trsitana you need for a level 3, when enemies have full level 3 and 6-10 items.
If Riot really don't want to fix the items drop, and reroll and carousl are as shitty as the rest of that gamemode, at least something to be made correct and with decent chances to have some consitency.