I'm 57, I laugh at this author just as I do with everyone else that believes this. The rate of good quality music being produced hasn't changed. The medium that brings it to our ears has, and it fills them with crap if we just turn on a radio or SiriusXM as our choices of content.
I like classic rock, if somebody decides that's what they want to listen to, I'm perfectly fine with it. I grow tired of listening to familiar music, so, I choose whatever fits my mood.
I believe pop music has been ruined by Streaming and satellite radio due to the lack of fidelity in their modes of transport. When XM appeared in the stores as an accessory for your car, I was walking around Manhattan playing home recorded cassettes through a decent walkman and Koss PortaPro headphones. I came upon a Sony XM unit in a store, working, with a headphone jack, hmmm. I plugged in my headphones, found a music channel and "meh", tried another, and another, "Are they joking?!" The music quality was somewhere between AM and FM playing through a 9 volt handheld. Like mp3 recordings, weren't any better. I also discovered my wife and kids didn't care if XM or mp3s didn't sound as good as a CD.
On the road, the satellite radio is acceptable quality, but, I haven't found a single station I can tolerate for even an hour. The playlists are either boring or irritating.
I've had a Pandora subscription for a few years. Their "Nusic Genome Project" provided decent playlists to start from. The player lets me look back on what played, vote yay or nay to tailor the list and also search out an artist for more music and more artists. They also added a stream quality option. I have it set to high and it's noticeably better than standard. When I use Bluetooth in my truck, it's better sound quality than SiriusXM. At home, my Yamaha receiver came with an external Bluetooth adapter, I've since upgraded the adapter to a unit with LDAC and it streams 96K/24 from my Samsung S22 Ultra to my receiver, which I set to direct (processing bypassed) to drive a Parasound A21 to AR303s. I also have music I purchased, stored on my phone, in flac 96K/24, that I can stream as well.
I've noticed the music quality streaming from Pandora is generally good, but the sound quality varies, from sounding like a low bandwidth mp3 that my daughter found on BearShare, to sounding as good as the 96K/24 Hi Res works that I bought from HDtracks. Since the Hi Res streaming services have made it to prime time, I decided to check them out. I discovered the same problem. It isn't the bandwidth limiting the sonic quality of the music anymore it's the engineering applied to the recording. I imagine it boils down to how much control an artist has while producing a record and how much they care about the playback quality delivered to the public.
Since I've discovered Internet and streaming, I've listened to many genres of artists, old and new, that I haven't heard before, and I really enjoy what's out there. I've been enlightened by vocals, Jazz, Blues, roots rock, Americana, folk, rockabilly, swing, and fusions of whatever. I haven't searched for classical (maybe someday). Most of what I listen to isn't played on the radio or SiriusXM.
So, if you think nobody makes good music anymore, you haven't really looked.