Consider this:
We start with 23 cards in our deck, which is 30 - 7. You'll have more if you're a stally deck.
As a result, it takes 23 turns to die from deckout.
This card halves that to 12.5 turns, assuming you get one out on the first turn, which is impossible but nuance makes stuff complicated.
100 / 12.5 is 8.
Therefore, it is safe to assume that a single copy of this card is as good as a single creature with 8 ATK, give or take complications.
This maths gets weird with multiple copies, fails to factor in how you can only have 6 scorpions but many more cards that also deal damage as well as you not likely to get a scorpion out until later, and how milling affects the board more than being hit in the face.
You would be hard pressed to balance out an eight-damage fighter that also messes with your opponent's draws.
Milling is just one of those mechanics that fundamentally can't work with current ETG's system. If it was less than six copies of a card per deck, it could work. If it was minimum deck size 40, it could work.