'Simplistic' and 'simple,' 'fulsome' and 'comprehensive'

From a brief I just read:

Plaintiffs have stated claims for the violation of the Second Amendment-the right to bear arms. Such right is explicitly spelled out in the Constitution, and has been even found to be a fundamental right by the Ohio General Assembly and the Ohio Supreme Court. [Citations.] This simplistic argument clearly refutes and defeats the motion to dismiss.

"Simplistic" isn't just a fancy way of saying "simple": In the words of the Oxford English Dictionary, it means "Of the nature of, or characterized by, (extreme) simplicity. Now [usually] with the connotation of excessive or misleading simplification." Not a good thing to say about your own argument.

Even if "simple" had become, through usage, an established alternative meaning for "simplistic," I would still have counseled against using that meaning. Using the term "simplistic" will bring the negative connotation to the reader's mind, even if there is an alternative meaning with a positive or neutral connotation. For instance, though "fulsome" has regained its archaic meaning of "abundant or copious" or "comprehensive," as well as meaning "offensive to good taste, especially as being excessive; overdone or gross," "disgusting; sickening; repulsive," and "excessively or insincerely lavish," any use of it will likely bring up the negative connotation to some readers, even if they quickly realize that the writer intends the positive definition.

But as best I can tell, "simplistic" has not even acquired an established alternate meaning of "simple." Using "simplistic" to mean "simple" is contrary to common usage, even though the error occurs often enough that lexicographers have noticed it.

I assume, by the way, that such errors generally stem from some people's tendency to try to use the fanciest versions of simple words they can find, as in "utilize" to mean simply "use." That's bad enough when the fancy word at least has the right definition, but often it leads people to use a fancy word with the wrong definition.