Also 4 AC is a lot...
A 20% decrease in hit chance for your enemies. If you assume that they have the average hitchance 5e is designed around of 60%, this cuts them down to 40%. A +2 magic shield is a 33% increase in survivability, a good off hand weapon can't hold up with that.
Although they are much better than usual in this game. Two handed weapon fighting shines before level 5, as it is the only way to get 2 attacks per turn then. And in the late game there are enough one handed weapons with on hit elemental damage to make them a viable option next to sword and board and two handed.
In normal 5e play dual wield is pretty shit, here it is ok. But not significantly better than the rest, except for rogues. It is really good for them, since it gives you a second chance at sneak attacking.