This card works better in decks with more creatures, and at the moment, mono-life rush gets countered by about everything. Playing that deck itself is the drawback.
That's a lie. I was in the top 50 in Silver Arena using a mono-life rush, and it stayed in the top 100 for like 6 days, until it's HP was at 34. Mono-Life is a great deck.
And no, I didn't use upgraded cards, either.
Besides, it's basically like Electrum Hourglass - just that yo can use it at most 50% of the time, so it's way weaker than EH and thus balanced. The only thing one could say is that it should cost unupped, in comparison to EH.
He said that drawing cards have a drawback close to the heart of their element. I think if each Great Oak lost 1 hp per use of ability, then it'd match the element. The tree gave some of it's life to try to make a new one.