My intention is to explain that all writing (as an activity) is advertising (as an activity). Same goes for the second sentence.
Does this sentence convey an explanation mentioned above?
All writing is advertising. Not all writing is a good advertising.
If I understand it correctly, both "Writing" and "Advertising" can be used either as a noun or a verb.
My writing on health was a huge success.
I saw a cool advertising on health.
... Is this a gerund? A verb that functions as a noun?
I am writing
Stop advertising yourself.