^ As long as the essay is unique and about you, it's fine.
Just saying something along the lines of "I like art, and Penn has x, y, z" is not going to make it a strong essay though, no matter how flowery you make it. You want a focused essay, and you don't want to be talking about ten different things. In that sense, it is good that you only talk about one major topic. However, I'm sure adcoms have read that topic ad nauseum. Give it a different twist so it's not just a overdone, cliche essay. You won't come across as one-sided, but your essay might not be memorable or personal.