He might be right about Spotify, since that company is a one trick pony, but he's wrong about the music industry in general. Most metal bands for example already put their music on youtube and other streaming services knowing that people will simply download it using other means anyway. The way they make money is through live gigs, merchandise, and various online sales. One way or another, streaming is already irrelevant to most musicians; unless you're in the top one percent, you're not going to make a living out of Spotify or Apple Music. If you want to make money, you need to know how to connect to people on an intimate level, and create an on-line following willing to buy your stuff.
You're absolutely right, but this isn't even unique to streaming. Selling copies of your music, whether it's vinyl, 8 track, cassette tape, CD, MP3, or streaming, has never been a primary source of income for the vast majority of musicians. It's a marketing tool. Most of them are thrilled just to break even on selling an album. I talked to Nick Waterhouse after a show last year about this topic; he tours to make money, and his tour was funded by a single car commercial one of his songs was in. Album sales didn't even factor into the equation.