It's not surprising. With content providers creating their own streaming platforms and with the costs of streaming rights for movies and shows going up it's not surprising Netflix's catalog has shrunk substantially over the last 4 years. I honestly saw this coming back when I first subscribed to Netflix because it was only a matter of time before others took a page from Netflix's book and started doing the same thing. Honestly I don't know why I pay for Netflix anymore. I rarely, if ever, watch anything on it anymore (and when I do it might be once every few months) besides certain shows (like Supernatural, I really wish they'd get season 11 up) and documentaries (I absolutely love Netflix for documentaries).
Honestly the only thing that will keep Netflix going is their original content they've been creating over that last few years (stuff I have yet to watch but I do plan on checking out Stranger Things, Orange is the New Black, and House of Cards (which I've heard nothing but great things about) to name few). I tend to download all the movies I want to see if I don't get to see them in the theater and before I buy them (I buy very few movies without watching them and only if I know I'll like them (like The Hobbit Movies and what not)) and I do the same with TV shows since I rarely watch anything on cable anymore (again there are exceptions like Deadliest Catch but that's one day of the week).
I've never used Sling but I haven't heard good things about it from the few people I know who use it. I've been looking into getting Playstation Vue (I've heard nothing but good things about it) but I'd run into the same problem I do with cable/Netflix, I'd rarely watch it so it'd be a waste of money (luckily I don't pay for cable so that's one bill I don't have to pay). Honestly the one thing I do spend a lot of time watching content on is YouTube, thankfully that's free (for now, who knows what may come down the line).