Assumptions – How to add a vector variable to a vector value?

If we have a three-dimensional vector variable:

$ Assumptions = a ∈ Vectors[3];

and a three-dimensional vector value for example:

b = {1, 2, 3};

then a + b makes {1 + a, 2 + a, 3 + a}. It is planned to generate a + {1, 2, 3}because it can not reduce the equation unless you know the names of the vector components. It seems that Mathematica recognizes a like a scalar.