You know you don't have to kill them, right? These are just characters. All you need to do is kill your opponent and you will win.
You do indeed have to kill them if you don't want your opponent to completely paralyze you, which most of these cards do.
Are you sure your opponent has a Hero in his deck? Maybe he's playing some fast rainbow and doesn't even have a Hero. Can you directly even target a Hero or not? I don't know, maybe you can't?
If you can't target a hero why even bother playing after the opponent gets out a card that automatically kills all your creatures and hits harder than dragons that you can do absolutely nothing about? And it wouldn't matter if you only saw a hero in 1/4 of all decks, because that's still 1/4 of all your matches being losses the instant your opponent plays a hero and you aren't prepared to stop it in two turns or so.
So after that highlighted part you STILL went and explained to me why they aren't balanced?
The point is not that these aren't balanced, the point is that I doubt anyone could go back and balance heroes on this scale. How do you balance a creature that automatically kills everything the opponent plays just by existing? Are you going to make it easily killable? Would it still be worth 20 quanta them? And after you make both those changes, is it still good enough to compare with all the others? Sticking unkillable super-duper-ubers with ****-you-up-totally spells into a young and already imbalanced card game with an already heavy amount of draw luck involved is just not going to benefit the gameplay. Adding more things that need to be countered when the game is already too specific with many of its counters isn't going to help the game's polish.
If there are going to be heroes, they should be slightly stronger than a normal card, not something that wins by itself. I actually thought the current set of upgrades are mostly good hero cards, a little weak if only one is allowed per deck, but those are considered standard now.
I think you are missing the big picture here. You are saying that having powerful cards would somehow be impossible to balance. That's not true. What if they cost 100 quantum to play, would they still be overpowered? I don't think so. What if they cost 25 quantum? Who knows. What if kept the cost where it is but made Hero's less powerful? What I'm trying to say is that there is always a balance. You just have to find it.
I just have to find it? No, you're the one who wants heroes, you go balance them. But I will say that putting a super-high cost on a super-powerful creature is just so much more likely to end in disaster and a favoring of luck, one way or the other, then putting a medium-high cost on a creature with slightly stronger than average abilities.
I laughed my ass off at the Chosen One's portrait but if these aren't really serious card suggestions (which you seem to suggest with your comment about spending lots of time designing the cards and no time considering their stats) you need to make that clear, and if they are the burden is yours to balance them.