You’re absolutely right that working with clients is the most profitable way to be a writer!
You can find clients so many places outside of Upwork (and similar) and generally will make a lot more money by working with clients directly.
You shouldn’t be ashamed or find it difficult to say “I am a writer.” It is simply what you do. When people as “Oh, what do you write?” Just respond “I do a lot of copywriting and blogging for various companies.”
Constant Content, Upwork, Bloggmutt, etc. Personally I do not like these types of content mills, as I think they perpetuate a cycle of going with the lowest bidder and devaluing freelancers.