What you are describing here is approaching usability. And when it comes to usability simplicity doesn't matter on its own, there are four other things to always keep in mind together with simplicity: consistency, flexibility, universality and familiarity. And then understanding what users need your piece of text for applying those concept to come up with the best balance to make users think and learn as little as possible throughout the whole lifecycle of the use.
Take, for example, familiarity. If you use a richer vocabulary that your users already familiar with, they certainly wouldn't need to learn more words and the piece with richer vocabulary would be easier for them to go through, than the longer piece with poorer vocabulary.
Simple doesn't mean more usable, but it's a pretty straightforward concept to understand, there is no confusion around it.
Take, for example, familiarity. If you use a richer vocabulary that your users already familiar with, they certainly wouldn't need to learn more words and the piece with richer vocabulary would be easier for them to go through, than the longer piece with poorer vocabulary.
Simple doesn't mean more usable, but it's a pretty straightforward concept to understand, there is no confusion around it.