I'm sure for greedy part they make more money with higher rarity card so that's why its unbalance in number
Transfert all the "Easiest" Mechanic to Common.
Card need a bit more skill to Rare.
Card that have multiple effect like "the witch" to Epic
Card having a Unique gameplay mechanic to Legendary
example "magic archer, miner, fisherman"
This way it will be easier to build a deck. It will balance the rarity because its stupid to have more rare, epic than common and legendary are catching common card.
A Simple Update
Like the update that fix every card Level to 13 its just a simple math multiply
I dont know if it will reach any good eye from the company but i would like a respond on the idea