I disagree and think this is changing rapidly, especially in the electronic/EDM scenes. In these arenas, a lot of careers blossom from SoundCloud, YouTube, and having other artists/DJs pick up tracks and play them in their sets. Marketing is still a factor but matters a lot less (many artists even wear masks/helmets). A quality track can (and many have been) made with just a laptop. Martin Garrix released his first hit "Animals" at age 16/17 after one his remixes was picked up by another DJ.

Additionally, music discovery has fundamentally changed because of streaming services like Spotify, as well. Just a couple of days ago there was an article on the front page of HN about how the top 40 tracks on Spotify make up a smaller percentage of the streams than even a year or two ago. Discovery features allow tracks to rise on their merit/listening stats making marketing much less important than it used to be, across genres.

With that said, it's still hard to make it. The barrier to entry has never been lower and thus there is a tremendous amount of competition and talent to contend with now. The determining factor for winning these days seems to be the ability to consistently and reliably release quality tunes over and over again.