Rotation as a vector
While I'm not an expert on mathematics, anyone can have an opinion. I don't think opinions should be just for experts.
I asserted that a angular displacement could be represented as a vector because it seems clear to me.
A rotational displacement can be completely described by its magnitude and the axis of rotation. All of the information about the rotation can be expressed as a vector. A body (or coordinate system) rotated 10 degrees cw about the x axis could be said to have an angular displacement vector of magnitude 10 degrees & direction towards the positive x axis.
I assert that all of the information about the angular displacement can be represented as a vector (if one wanted to represent angular displacement in this way). Not necessarily that is should be represented in this way.
However, I expect that there are advantages in representing rotational displacement as a vector in that it parallels the representation of linear displacement. Also, some of the principles of linear motion and Newton's laws would apply to rotational motion as well if angular displacement, velocity and acceleration were all represented as vectors.