I agree and disagree with this point. Yes, the actual content and self-reflection in your essay is more important than the flowery language or intricate grammatical structures that you use. But a good application essay can be about pretty much anything, as long as you are reflective enough.
Don’t think about a personal statement as “an essay about something.” Think of it as “an essay about you”—the theme that it uses, whether that be Covid, your favorite hobby, or how you learned to ride a bike, is merely the vehicle through which you’re talking about yourself. If you can make that “something” into a window into your mind, then your essay is golden.