This screed is a dandy example of the prescriptive mentality described by the linguist, Steven Pinker in his book, The Language Instinct.
These folks are "Kibbitzers and nudniks", they most assuredly are not language scientists. See the great description of them and their prescriptions/false language rules below in the second quote box.
This describes "off of", which Centrox also seems to have a problem with. It is not different than the original asked by Paok, "of a ...", which is used by US and Canadian newscasters, hosts of TV cook shows, mayors, newspaper columnists, Flannery O'Connor, Henry Adams letter of 1859, ... .
Let's take a quick look at Centrox's totally contradictory advice. Advice that illustrates he doesn't even understand how language works. [my comments are in color, Centrox in black text.]
Centrox: No. never say (or write) that! ...
Linguists call the use of an additional 'of' the “big of” syndrome.
Linguists say no such thing. No source, Centrox.
M-W says, " Off of is an innocuous idiom - a compound preposition made of the adverb off and the preposition of -- that has been in use since the 16th century. In use since the 16th century is the very definition of "idiomatic".
Kenneth G. Wilson, wrote in The Columbia Guide to Standard American English in 1993, that although “how hard of a job” is nonstandard English, ... that nonstandard “of a” usages “could achieve idiomatic status before too long, despite the objections of many commentators.”
"commentators" = prescriptivists/kibbitzers and nudniks [as described by S Pinker] who get their panties in a bunch over things that are perfectly natural everyday idiom. As M-W noted, it is "an innocuous idiom ... that has been in use since the 16th century".
Until then, he said, they should be left out of “your Planned and Oratorical speech and your edited English.”
Centrox says, "No. never say (or write) that!" and his own source says it should be left out of “your Planned and Oratorical speech and your edited English”.
But there is no reason to leave it out of your everyday speech because, as all of language science says, it is idiomatic English, has been since the 16 century!
The fallacies of language mavens
The legislators of "correct English," in fact, are an informal network of copy-editors, dictionary usage panelists, style manual writers, English teachers, essayists, and pundits. Their authority, they claim, comes from their dedication to implementing standards that have served the language well in the past, especially in the prose of its finest writers, and that maximize its clarity, logic, consistency, elegance, precision, stability, and expressive range. William Safire, who writes the weekly column "On Language" for the [New York Times Magazine], calls himself a "language maven," from the Yiddish word meaning expert, and this gives us a convenient label for the entire group. To whom I say: Maven, shmaven! [Kibbitzers] and [nudniks] is more like it. For here are the remarkable facts. Most of the prescriptive rules of the language mavens make no sense on any level. They are bits of folklore that originated for screwball reasons several hundred years ago and have perpetuated themselves ever since. For as long as they have existed, speakers have flouted them, spawning identical plaints about the imminent decline of the language century after century. All the best writers in English have been among the flagrant flouters. The rules conform neither to logic nor tradition, and if they were ever followed they would force writers into fuzzy, clumsy, wordy, ambiguous, incomprehensible prose, in which certain thoughts are not expressible at all. Indeed, most of the "ignorant errors" these rules are supposed to correct display an elegant logic and an acute sensitivity to the grammatical texture of the language, to which the mavens are oblivious.