Let's compare graboid evolving to shrieker.
1 + 1 turns = +6atk
If we look at it this way, the 1 probably contributes a +2atk, so 1 turn should be worth 3-4 atk at least. Your acorn idea needs 3 turns to fully come out. That means if it starts with 0atk, the final form should have around 9-12atk. With the 2 you spent, probably around 11-13atk.
Then compare that to dragon.
Is 2 + 3 turns = 10 ?
Oldtrees, you ninja'd this one. Instead of me rewriting it, what do you think of these amendments? They feel a bit better to me.
Okay, by your analysis, if 1 turn ~ 4 Atk, then:
(unupped) Acorn 0
, 0/1. 0: Grow.
(unupped) Sapling (no cost), 3/6. 0: Grow.
Oak (no cost), 6/8. 0: Propagate.
(upgraded) Acorn 0
, 0/3. 0: Grow.
(upgraded) Sapling (no cost), 4/8. 0: Grow.
Ancient Oak (no cost), 8/16. 0: Propagate.
So, unupped, 1st turn cost 1 card, 0 dmg dealt. 2nd turn [1 card] cost, 3 dmg dealt. 3rd turn [1 card] cost, (6+3=9) dmg dealt. Average: 3 dmg/turn, as with Spark; 1 card|3 cards, 3 turns|1 turn. Delayed, but resilient. Is a turn worth roughly a card slot?
Upped: 1st turn cost 1 card, 0 dmg. 2nd turn [1 card] cost, 4 dmg dealt. 3rd turn [1 card] cost, 12 dmg dealt. Average: 4 dmg/turn, less than BL, but far, far more resilient.
Does that look a little better?