I completely agree that the perverse idea that, as soon as you've got a big user base, you must necessarily join the ring and fight for the world-streaming-championship-belt cost a lot to soundcloud and they kind of missed the point of their own strengths.
I've always seen Soundcloud as a sort of "music twitter", where you can sort of share bleeps and bits of your work, and give a general idea to your followers of where you're at, at THAT moment in time, and let them go somewhere less noisy and crowded (like bandcamp or your website or any other place) to focus on it if they're interested, just as you'd share links to other places on twitter, and just use the microblogging to situate yourself regarding what you just posted. Interestingly, I think recorded music is even more suited than speach/discourse for this kind of service, as a form of expression being by definition limited in time, when twitter really changed and shaped the way people talk about things on their service by limiting their capacity to blog more than 140 caracters. Also, both those websites are yet to find their business model and struggling with money and growth despite a huge and very dedicated userbase.
So really, for me Soundcloud thinking they can compete with Spotify, Apple Music or even smaller scale streaming services like Deezer, it's as if twitter was claiming they're gonna take down Facebook in the coming decade, absurd.
But to my knowledge, there isn't any other website right now, with soundcloud's user base, qualitative interface (I like how soundcloud interface behaves even though the last few years haven't always been for the best), and possibility to post anything on your own, without third party aggregators. Mixcloud isn't nowhere near that, and from what I've seen of it, it adresses more the DJ needs than musicians / composers, and other alternatives are yet to take off. From that point of view, I really hope SC find solutions because if it were to disappear it would really leave a big empty space, but I can't say I'm too hopeful about it.
That's also part of why Bandcamp's constant improvement feels like a breath of fresh air.