Love the idea too. But not tying specific set upgrades to character levels like it currently is. Personally I think you should simply earn an exclusive currency that is only used to upgrade cards. Instead of upgrading set specific cards at each level it just gives you so much of this currency to upgrade a card of your choosing. Obviously higher rarity upgrades should cost more but having the choice would help so you can tailor a specific deck earlier. Sorry, got a lil wordy there.
I've wondered about this a lot.
Levels means a reason to keep playing the game, mini-rewards along the way. Fine.
But the actual effect is that new players will not be able to compete with higher levels players...so where does the new revenue come from?
Doesn't matter, new players should not reach rank 1~5 until they gain at least level 30.