I've seen PVP druids torn apart by skilled players who know how to take a tree down. It's not that hard. It's called Teamwork...it's when people fail at it that trees become a problem.
EDIT: In fact it's not the druid in TREE form that even is a real problem.
teamwork? In WoW? unless you're running a premade, good luck with that
in arenas trees were easier to deal with because you have more coordination options, but that doesn't mean they aren't a pain in the ass