***** NOT A TEACHER *****
I have never taken a university-level class in syntax. My only "knowledge" about grammar is limited to high-school (secondary) level textbooks. So I will very timidly suggest a few ideas (certainly NOT "answers.")
1. "God bless -- no harm in a blessing -- the Pretender."
a. That sentence comes from one of my favorite books.
b. "No harm in a blessing" is clearly parenthetical.
c. As is obvious, it has no grammatical connection to either the subject or the predicate.
2. "Becoming a great writer -- or even a good writer -- requires practice and patience."
a. I think that we should ignore the hyphens when we analyze it.
b. Apparently, the writer used those hyphens to slow the reader down. It makes the statement more dramatic by pausing after the first "writer" and the second "writer."
c. The main point, IN MY OPINION, is that "even a good writer" IS grammatically connected to the subject.
i. Let's rewrite it without the "dramatic" hyphens:
"Becoming a great writer or a good writer requires practice and patience."
If I am not wrong, "a great writer or a good writer" is a compound object of the gerund "becoming." (Don't be misled by the author's punctuation.)
My source: House and Harman, Descriptive English Grammar (copyright 1931 and 1950).
Student or Learner