I've seen a lot of people on here be teased for difficulty expressing themselves. Either people complain "you're using big person words to describe mundane things" when they're aiming for precision or "woah, we don't need that damn wall of text" when they're aiming for clarity. It's like people just want to complain.
I don't think poor clarity is tightly coupled to vocabulary. Poor clarity often comes from extra words and poorly organized text.
"John walked to the grocery store"
vs
"The man known in his building, but not throughout the entire city, as John, took it upon himself to walk the winding streets of Brooklyn on foot until he reached a open storefront that sold mostly, but not exclusively, groceries"
The latter is pretty limited in vocabulary but is a mess.