EDIT: 1.5 is bringing in some changes to the 2H Skill line, so you may want to log on to the PTS (it will require a download if you do not have it already) and try the new stuff out before you change out that weapon.

Area of Effect. When the Skill Tooltip says Enemies rather than Target, then it means you are affecting more than one mob in the radius of the skill.

DKs don't have a lot of Built in AoE, other than Inhale and Sea of Flames.

For AoE, the best weapon is a Destruction Staff. However, I took my DK all the way to the VR Ranks (with 1 Hand/Shield) before I even gave him a second weapon to use. And that second weapon was a Destro Staff. This is also an excellent ranged weapon as both your weapon choices are for up close and personal. I think having a Ranged and Close in choice is better.

Which leads me to my next point. As you have discovered the 2 Handed Weapons are slow. To slow even with their higher damage. But, you also don't need to hold down your heavy attack (left click) for the entire animation to get a heavy attack. Not sure exactly how long you do need to, as I gave up on a 2H weapon along time ago. But, I use a 1-2 count and release and get a Heavy Attack. This is known as Animation Canceling in case you were wondering. You can also do this by winding up the heavy attack, then use a skill from your skill bar before the animation is done. It take some practice to get the timing down.

However you may find that a 1H/S is a better weapon to use on the DK. Its all mine used until VR Ranks before I added the Staff. You can respecc your skill points if you want to change up your skills. They build up rather quickly if your fighting mobs near your level, so it won't take long to grind the new skill up.