Something comes over most people when they start writing. The sentence structure and even the what makes you human essay are different. No one uses “pen” as a verb in spoken English.
Ok, so written and spoken language are different. If you want people to read and understand what you write, yes. Written language is more complex, which makes it more work to read. You don’t need complex sentences to express complex ideas. But even those they use no more than necessary.
Informal language is the athletic clothing of ideas. I’m not saying spoken language always works best. It seems to be hard for most people to write in spoken language. I’d say this if I were talking to a friend? This trick may not always be enough. For cases like that there’s a more drastic solution. Then replace the draft with what you said to your friend.