Differences between the mounts

I have managed to reach level 20 inquisition and couldn't get any more inquisition experience with the special items in Skyhold.

I remember reading somewhere (having trouble finding the source now), that each character has their own unique armor model. Basically, whatever item you equip on your Inquisitor - it will always look similar (except for colors). Equipping the same item to one of your companions, will make it look like their personal model.

Due to this fact, it is not possible to have a plate armor look for your mage, since the mage unique armor looks for you and your companions are generally cloth-like.

There's a masterwork item that removes the armor requirement on the crafted item, effectively allowing a mage to wear heavy armor. However, due to the fact stated above (which I tested in-game, to my disappointment), the look of the armor will change to your character's unique look.