Writing should also take into account it's audience. You aren't going to write a technical book about quantum mechanics designed for experts in the field and use high level terms and explanations. It would almost be insulting to the experts' intelligence who decide to pick up and read the book. On the same token, you don't want to fill a book with a ton of low level technical talk and jargon in a book designed for beginners who lack any in-depth understanding.
When it comes to novel writing, it isn't so cut and dry. On one hand, you have the author wanting to show off their ability to write, portray beautiful scenes, and sound like an expert writer by correctly using big terms and literary elements. The reader just wants to read a well written story. Whether it is simple language or not isn't so much of the issue. What matters in the end is how the words are used.
Take martial arts for example. When a fighter wants to show off their skills and be flashy, they will do all these flips and moves and twists and turns that look really really cool. When it boils down to a real fight though, 90% of that will be replaced with simple kicks and punches because it is what is practical. A simple punch is just as effective if not more effective than adding in the flare.
Another example we can use is music. Some times the most beautiful piano song we can hear sounds so elegant, so moving, so robust. When you go to look at the sheet music, you are almost half disappointed to find out that it is rather fairly simple to play and feel cheated that something so beautiful was so simple.
In sports, we often hear analysts judging struggling players. The most common advice heard is "they need to get back to the basics and fundamentals" or that they "need to remove the unnecessary movements and simplify it".
It all boils down to you. Are you able to write a masterfully simple piece? Or are you able to write an decent but complicated piece? Doing things simply but masterfully will always be better than struggling to do things complicated. In the end you need to find your comfort zone and balance in the spectrum of it.