Publishers focus on LAUNCH – and pretty much everyone gets help with pre-launch/launch publicity. What they do exactly varies. ARCs, reviews, marketing – some of it indies can do, other stuff they can’t.
Publishers don’t care whether a writer is a hack. They care whether a writer will make a profit for them. You listed two writers who made a LOT of money for them. That money is what enables publishers to take a chance on unknown writers.
Whether you trad pub or not is a personal decision – and it depends on what you write and what your goals are. I write book club fiction; self pub would be the equivalent of burning my manuscript. My books need access to things (like book boxes, box stores, book clubs run by celebrities, etc.) that self pub doesn’t have access to. Trad pub can give me that, though.
On the other hand, if I wrote adult genre fiction, I can’t imagine I would try to trad pub it (unless it was standalone). Definitely not an adult genre series. Why? Because trad pub pays crap for that, and the audiences are RABID. I can make way more self pubbing.
Marketing isn’t the only benefit that trad pub has. Don’t discount their reach to places self pub still can’t access. Writing middle grade or YA? School libraries, public libraries, Scholastic, book fairs, book subscription boxes… THOSE are what you need, and you CAN’T get to them as a self pubbed author. Not en masse. You can hand sell to a book store here and there, a library here and there. But that’s NOT the same as what trad pub would get you. Plus speaking engagements with your target audience!!
Trad pub and self pub are both viable, but they’re not equally good for every book.