I do agree that art is a way of expressing what an artist him/herself is attempting to portray, regardless of whether it is through painting, sculpture, poetry, a play, or simply through music.
While this is true, what I do think is missing when it comes to defining art as a whole is having enough people to truly grasp the deeper aspect of the artwork they see in front of them and to truly pay attention even to the smallest detail of the piece itself.
And I am speaking from an subjective perspective because over the years, I have come to truly appreciate the creativity and the effort each artist has put into their own masterpieces, especially when it was through various mediums.