That is completely untrue.
When I as 20, my musical taste was near-completely limited to "West Coast Rock" and Soul. Then I discovered Ska when I was in my early thirties. It's now one of my favorite genres, and that includes stuff like Japanese girl band ska, which is about as far away from "West Coast Rock" as it can get.
Really, really, really, please speak for yourself.
No, it opens me up to the stuff that I usually wouldn't buy. Why is that automatically mediocre? I am currently listening to stuff that I never felt like buying, but it's certainly not mediocre. In fact, it's probably someone else's favorite music.
I can now listen to hundreds of album cuts from great jazz musicians. Before, I would have had to buy a hundred albums from these musicians to do the same thing, hoping to find some gems on these albums. I didn't care enough for jazz to do that. But I am sure that there are people here who'd tell me that I was missing out on some of the greatest music ever made. Well, perhaps they are right, but there's simply a limit to what I am willing to spend on music. That doesn't mean that the stuff that I am not going to buy is not good.
Everything you are mentioning about "discovery" is available to you right now, for free, and has been for years. There is more discovery at our fingertips than ever before.
Apple Music is nothing new. It's a conglomeration of Spotify, Pandora, Twitter, YouTube, and iTunes. The world didn't stop revolving because of these services in 2012 so why should it stop now? Because Apple put it into one bloated app? Heavy downloaders and 'discoverers' can enjoy Apple Music and if they want to ditch Spotify and the other services that's cool. But for the average listener, this is just yet another way that Apple is trying to re-purpose iTunes and it's not good for the consumer; it's good for Apple and the record companies. And that's counter to what Apple used to be like. We're all about over-paying for quality. This isn't quality. It's just saturation.
BJ