HBO seems to be doing fairly well. They have ~5 million online subscribers, up from 2 million in Feb. 2017. That's small potatoes vs. Netflix's 117+ million subscribers, but it's a nice growth rate for a premium product. We don't have cable and are happy subscribers to both HBO and Netflix.
It's funny you don't even mention Apple. We used to buy seasons of TV shows off of Apple when they weren't available elsewhere, but don't anymore because we can't watch them on our Roku (at least I don't think we can).
HBO's has higher profit margins, but lower revenue. Further, being tied to Time Warner complicates the issue, without cable HBO would fail. So it's in a race to add subscribers fast enough to keep up with cord cutters.
It's really a content issue for me as last few times I checked they had nothing worth watching that I have not already seen.
A small number of shows are not included in our No Commercials Add-on. You can still watch these shows, however, they will play with a short commercial before and after each episode.
While the list of shows may change, they are currently: Grey’s Anatomy, Once Upon a Time, Marvel’s Agents of S.H.I.E.L.D., Scandal, Grimm, New Girl, and How To Get Away With Murder.
And then on top of that it's a wasteland content-wise as you stated.
HBO go is struggling and heavily dependent on dwindling cable subscribers to keep HBO viable.
Amazon video is similarly subsidized by Amazon. Treated more as a loss leader than a profit center with ~1/3 million of Netflix's subscribers even though it's included with an Amazon prime subscription.
Netflix does not have total dominance, but with a solid track record of original content and a massive subscriber base they are becoming harder to beat over time.