I'm writing this because I just got yet another rejection from a publisher. There was no mention of the actual quality of the manuscript. They're only complaint was that they require "an established web presence such as a website, social media along with noticeable effort to engage potential readers prior to publication".
What the publisher is saying is that once you've built an audience they'll be interested. I'd run away from this type of publisher. They want you to do all the work of building an audience and then reap the major part of the reward.
As far as exposure for an author goes, social media is just one piece of an entire marketing strategy. Its best purpose is for customer retention (people who've already bought one of your books and liked it enough to follow you on FB or Twitter hoping to find out about new releases and such). The second benefit of social media is word of mouth advertising. When people come to your page/timeline and like your posts or talk to you their friends see the interaction, which gives your work exposure. The third benefit is networking with other authors (if you're so inclined). Networking allows you to do things like newsletter swaps where you both (or many authors) put your books on sale for .99 or free then everyone blasts their newsletters about the sale.
For ideas about using social media go look at some other fantasy authors' FB and Twitter feeds. Look at what they're doing. Maybe some authors in this forum can give you some tips on what's working for them. I know that one author here is slowly building his social media presence. Maybe he can tell what he's doing and how it's working. I don't want to out him, but his name rhymes with Hustan Jenner.
For exposure for your books I think you need to take some time and build a marketing strategy. I say this in all the kindness I'm capable of (which isn't much), but it looks to me like you've tried a bunch of tactics without any underlying strategy. Kinda like an army shooting some arrows, sending out the cavalry, and forming up the infantry without an objective.
So, first ask yourself, "What is my objective?"
-- Is it selling books?
-- Is it building a niche audience that will read everything you write?
-- Is it building a brand that a wide audience will enjoy?
-- Is it getting traditionally published?
-- Is it selling the movie rights to HBO or Netflix? -- ok, a guy can dream, right?
Then build a plan (strategy) to reach that objective. If it's just selling books you don't have to do much more than write a decent series and use Amazon advertising to sell the first in series. You'll lose money on the first book, but make money on the people who buy book 2, 3, 4, etc. (assuming the books are decent). If you put your books in Kindle Unlimited you'll get an added benefit of more exposure and page read payouts. If you're making a little money use it to ad FB and other advertising. Then write the next series, rinse and repeat.
If you're building a niche audience or a wide brand, your strategy will have to start with a lot of research about your intended audience. Then writing a series specifically designed for them. Then using advertising tactics that find that specific audience. Then building an ecosystem (website, social media, forums, newsletter, etc.) that keeps your audience aware of you and your new works. Each time you release a new book you'll get a boost of exposure because your audience will be talking about the new release on social media.
Long story even longer, define your objective then build a strategy using the proper tactics to achieve the objective. This will take research and a lot of thinking about the best use of each tactic, but it will probably work better than throwing tactics against the wall to see what sticks.
