It's not because in the past (I mean 500 years ago) art was produced by doing something different from what existed that you should conclude that "art is about

It's not because in the past (I mean 500 years ago) art was produced by doing something different from what existed that you should conclude that "art is about being original", even less that "art is revolt against what was previously done". These facts, if always true, are just consequences of another, much higher, goal of the artist. It's because modern artists started thinking that _the goal_ of art was to be original that we came to this situation.