Youtube has become very commercialized, true, but you can still use it exactly like SoundCloud, can you not? Just ignore the ads and recommendations and it's basically the same experience.
Although, it does seem like SC is a cleaner, more targeted audio platform.
As I mentioned below, SC is limited to 128 mp3. Put youtube in 720p and the audio is decent-bitrate AAC, pretty much transparent. This is SC's most glaring and easily-fixed problem.
The low quality is actually a boon to established artists, it gives people an incentive to buy the record rather than streaming it again and again. For unknown people trying to promote their sound, not so much.
Part of the problem is Google's stinginess over bandwidth. They keep hiding the stream quality option more and more (referring to Google Play Music as well as Youtube) and they are literally RUINING the music. I've had to put HOURS of manual effort into changing stream quality on Google's products.
I wouldn't say it's the same experience. Youtube is cluttered and music is a side offering, primarily in the form of music videos. Song-only videos have been notorious for being posted by somebody other than the owner and not existing reliably (copy infringement). Soundcloud makes a home for your song that can be shared forever, is pleasant to visit, and links you to tons of related music and explore the musical interests of other people that like that music.
Hmmm. I've been in the trap scene myself lately, and this is the trend I see. Soundcloud just works so much better because of the community, the ease of linking artists together (I love how rappers will feature other rappers, then you can go listen to that other rapper and explore an entire new world of music), the overall presentation of audio with waves, similar to an audio player (Google tries to do this more with Google Play Music rather than Youtube). Souncloud is just a much more polished experience for music.
Having a cleaner more targeted platform goes a long way. The bandwith consumption is a lot less on mobile and content specific communities often provide a more-targeted user-centric experience. They are quite similar, but sometimes being a little different, a little more focused, and more niche can go a long way.
edit: I also do not think these services are mutually exclusive.
Although, it does seem like SC is a cleaner, more targeted audio platform.