In my opinion there is nothing wrong with the Dol Guldur Orcs. Also, I don't believe changing visuals is a priority of the team. The case with the Dwarves is that they with the visual changes each sub-faction needed a new playing style as well.
Anyhow, I don't find your arguments very convincing. Especially the one considering armour, I can only say that with units that are used massively (all standard units, essentially) it is only a pain for the game engine to deal with detailed images, that is it becomes slower for us.
The banner carrier could give the units a nice touch but without any image reference I cannot know what that looks like.
The archers are perfectly fine this way, they are recognisable as Dol Guldur Orcs.
The poison attacks are also a clear indication of how these orcs have an offensive benefit opposed to the Morannon Orcs. The argument that Minas Morgul is more known for its poison is invalid, because it only exists through the Morgul blades and daggers that the Nazgul carry. You hardly expect regular Orcs to carry them, do you?
The trolls are a difficult subject of discussion. They are meant to be upgraded and upset the enemy frontline mainly, while also doing significant building damage. The fact that the upgrade is done in two stages gives people the tactical choice of sending in first the trolls that have only armour to upset the pikemen, and then send in another with armour and a hammer/sword to deal with other infantry.