Good additions @yoz.
Starting from “trivializer” (see @toddbarnard thread), I found “downplayer”, and this fitting definition:
“Downplayer: A word used to make someone or something look less significant.”
— from https://www.deanza.edu/faculty/ramireztono/phil04/weekfiveoverhead.pdf
Your examples “common X” and “standard Y” could be considered downplayer adjectives, except perhaps when in proper nouns like Common Lisp, Standard Oil, or if an actual standard (like HTML) is cited.