Write to your audience. If the audience consists of experts in a field, it is acceptable to write in an advanced level. But, in general, as a writer you must select from three possible levels. The selection should favor the second of the three.
The lowest level, using simple sentences and small words, does not indicate adequate intelligence to write formally, and brings one’s credentials into question. There is an assumption that if one is not proficient in English one is also lacking in proficiency in the subject matter of the article. People want to read the work of someone qualified to write in the field.
The proper level of an article is to use words that are carefully chosen for connotations as well as definitions. Choose words that are well known, but beyond the elementary school level. Avoid, as much as possible, obscure words, unless needed for a specific purpose. In addition, sentences should have phrases that clarify ideas where needed. Simple sentences with few adjectives and adverbs, and devoid of dependent phrases, gives too little credibility to the author.
The other extreme is to write in a pompous manner, using large words as often as possible. If the reader must grab a dictionary multiple times during a reading of an article, the work is not reaching the audience as it should. Writing is not to be taken as an opportunity for an author to show the extent of the author’s vocabulary. Writing is communication, and when one gets to a level where communication ceases the problem is with the author, not the reader.