I was recently lucky enough to find a small, reputable publisher in the UK who accepted my manuscripts. I was lucky he was looking to expand his science fiction line and that is what I write.
I was also lucky enough to talk with a top flight agent who is the daughter of a friend of mine. She told me the following. "First build up your social media followers. As a new writer, if you don't have enough, you won't even get through the door with any traditional publisher."
Having spent ten/eleven years writing a five-book science fiction series and getting it published, I now face the job of marketing. My publisher doesn't do a lot of marketing - it's too expensive. I also know for a new author like myself traditional publishers also do very little - especially in my genre.
Luckily since I have five books that will be published over the next two or three years I have time to try different approaches to marketing and see which ones work.
I do believe catching the eye of influencers is tremendously helpful and that booktok is a great marketing tool. The question now is who and how to attract the right ones to my work.
I am producing a book trailer so I think that will help. I'm not investing in it, my son in law, a talented designer is putting it together for me without cost. (I'm lucky).
You are right - it is very difficult to get anything published now which doesn't stand the chance of being a break-out book. Especially if you are a new author. It wasn't like that twenty or thirty years ago - I know I worked for a small press and we really looked for diverse, new authors, and helped them promote their books.