the aphoristic style,
the "5-paragraph" style,
the research paper, etc.
A paper should be as simple as necessary, but no simpler. Depending on your topic, you could have 20 paragraphs, 10 paragraphs. And if what you're writing is arguably good, length shouldn't matter. At some point in your paper you should say, "I'm doing a damn fine job here, and my professor should love to read this."
If you cannot say that, that is a good indication that you should dump the paper. Not some rigid, lifeless arbitrary numeral. Numbers are not out to get you.
Our education system in the West has done a serious disservice to us by installing this idea that we should feel bad about making others read what we write.
It's bloody awful.
You should use your topic as a basis for experimenting with different styles, not as a means to prove your mastery of the language.
Papers are not proofs.