Yes, the targetting is sometimes a bit hard, since people in front of your wanted target prevent that you can target it.
But i am absolutely against Tab-Targetting, that would make the fighting system boring and cheap.
If someone want to secure a friend, it must be possible to make him out of sight.
They surely have to work on the targetting, because even for PVE it is hard to fight at the actual state, but it should be an intelligent targetting.
Friendly units should get ignored as a target if you cast an attack skill, instead the unit behind should be in target.
Friendly units should be classified as target, if you want to cast a buff or heal.
That would help for PVE and for PVP aswell.