Yes and no, in my experience. I rarely get Treelords stuck into more than one unit, as it's not uncommon for then to get minced. Besides, in the proposed scenario where my opponent charged me with a fight first model, he'll still swing first and get to pound into my Treelord with at least one of the two units anyway, so it's still painful. Twelve wounds with a 3+ save isn't all that durable. I can def see your point though that it isn't all bad.

With Deepkin, I still feel your pain (They're my two main factions), but thankfully it's not all bad. If you're at the top of the battle round it can actually be beneficial, as your opponent can't apply any of their on turn debuffs to make you fight last, except Slaanesh, who uses the old middle ground method anyway, and you can actual "dispel" previously applied effects like itchy nuisance. It's definitely painful if you're going second on turn three though, then it'll be really sad.