Being overly simplistic is a character "vice of excess" stemming from what would otherwise be a character virtue in the form of elegance. It is intellectually narcissistic, which is to say that it contains either the intellectual narcissism of ignorance or prejudice. One may be ignorant of the maturity level of the audience for an elegant idea, underestimating their sophistication, and insulting them in a way that seems "patronizing." Or may they may be prejudicial against those who understand and process more complex concepts, mismatching and underutilizing the language of communication at their maturity level. It is then a common branding and marketing mistake made by novice marketers and other public communicators who try to get their ideas across to an audience they do not measure the sophistication and maturity of.
Someone who is "simplistic," is by definition, dumb down their complexity of communication to the point of losing the utility and power of their complex set of ideas. However, all human beings communicate on a spectrum between being overly simplistic, and overly complex to match the needs of their audience. This highlights the central psychological skill within maturity, which is the Observing Ego to scan the environment for its composition and needs, matching that to what we endeavor in that social environment.