No, "copywriting" is the act of writing "copy". The "copy" of "copywriting" is not countable; if you call it "a copy", that shifts the meaning of the word to "a reproduction". The act of writing or otherwise producing a copy is generally "copying", and the product of said activity is "a copy/reproduction/facsimile".
Copy here means "written text intended for reproduction." It is frequently used for advertising or media text, but not only that. For example, the contents of a book can be called "copy", and a person who edits a book for grammatical correctness (as opposed to content) is a copy editor (sometimes: copy-editor). A person who writes text that is used in journalism and advertising may be called a copywriter.
It would be rare indeed for a book author to be called a copywriter, so it is correct to say that a copywriter is writing copy for media or advertisements. It is not, however, strictly speaking correct to say that "copy" only refers to that content. It is a common term in publishing for the text body of unpublished material that is being processed for publication.
If you look at the edits and the discussion on that wiki article, you'll find there isn't consensus about how the word should be described or used and whether or not copywriting should be merged with Copy (written).
There was a change to the article around April 2015 that significantly changed the meaning of the definition and I cannot find any references to support that change. Every other definition I can find for "copywriting" defines it as an action, not the product of the action.
I believe that wiki article is wrong. Even wiktionary defines "copywriting" as the present participle of "copywrite" (that is to say: copywriting is the action of writing copy), itself listed as a backformation from copywriter (a word coined sometime around 1911 according to Merriam-Webster). None of the major dictionaries give "copywriting" its own entry, the ones that give example usages (e.g., Oxford) support my contention.
A better definition of copywriting is given by a couple of copywriter guilds.
American Writers & Artists, Inc says:
Copywriting is the process of writing advertising promotional
materials. Copywriters are responsible for the text on brochures,
billboards, websites, emails, advertisements, catalogs, and more.
The Copywriters Freelance Collective says:
Copywriting is in the first instance the creative process of
conceptualising advertisements and marketing devices such as events
and other platforms promoting brands or services.
A body of written works can be called "writing" or "the writings of So-and-so", but a body of news articles or advertisements is not "copywriting" and is most definitely not "the copywritings of Whosit".