What is the basis of the argument that there is no such thing as a realistic artist

There is no argument on that. There are lots of artists that can create a thing called realistic art. Still art and portraits are realistic if you make it to the exact items appearance. If that makes sence haha :)

The linear perspective changed the quality of art because it gave art a sense of reality. it gave the illusion that the background and surroundings were actually close and/or far and a sense of depth. linear perspective change the quality of art following its birth the renaissance period as they want the art to be more realistic and they believe one way to achieve it is to use the method of linear perspective. it uses the principle of math to realistically portray space and depth in art.