Im my (not so big) experience with the druid, the tree is really easy to destroy if opponent focus on it. A couple Force Hammer, Hurl Boulder, or Fireball, and maybe a melee strike to finish, and the tree will be over in 1-2 turns. And i find it diffucult to defend (apart from intercepting creatures, wich I consider at least medium investment in defences)
Easy to destroy... you are spending 18 mana on a 'couple' of force hammers.
You cant destroy it with 1 and a melee because the mage is guarding.
Dont forget... every round you delay the destruction of the tree is another 4 damage you have to do against 2 armor.
You make it sound easy - but in reality it is not.
I remember when i played my LoF warlock against a druid. I was laughing inside myself because the game would be so easy with the big bad boy doing flame attacks against his flame+2 units. Guess what. I got completely owned.
When i summoned LoF round 2 he countered me by summoning guarding angel round 3 with rouse beast so it would guard when round 4 started. In the mean time he got vinemarkers to my NC so my warlock was slow at getting to him with my lash. He also deployed 1 or 2 snatchers and a vine snapper.
It was not pretty. I was'nt close in accomplishing anything besides destroying a tanglevine on my mage.
I could have done a couple of things different, but it was the first time i tried that matchup and ever since that i have been shaking my head at the whine threads about druid being useless vs warlock.
If you want to kill the tree do so with few bigs. Dont invest in 2-3 attack spells because after they are gone you will be left naked against snatchers, raptors and snappers while the druid is pounding on you as well.