That's rather questionable assertion. Many people would not consider anything that's made by a "DJ" to be music, let alone high-brow one.
It also might be that you have only now discovered that there is something better than beyonces and x-men movies. That doesn't mean that there weren't anything good before, just that you haven't seen it.
But the thing is that I've looked and can't find anything nearly as good. Some artists brush up against it here and there (Glitch Mob, edIT, even Daft Punk, Weezy, or Kanye) but the density of really good work is no where near what it is today.
Speaking of Kanye, I actually think his last album was his best and that if he hadn't launched it with the following he built up when his work wasn't as developed (pre-Twisted Fantasy) his work would have a quarter of the following or less than it does today. He's one of the rare artists that keeps innovating after hitting it.
The only place I see at least some measure of really quality work in the past compared to today is fiction: Tom Robbins, Greg Egan, PKD, and many, many others. There are some contemporaries I like better (Ted Chiang) but I don't pretend it's not a matter of personal taste. But TV or music or even most film that's pre-2005 is almost unconsumable it's so flat compared to what the 1%-ile is today.
The internet has democratised music production and allowed us to have so much quality, self-published music that you'd never get in the past.
Technology has made music production so much easier and higher quality than before. I don't know much about non-electronic music, but I reckon for under a grand you could set up a half decent recording studio in your garage, and it's so much easier with computers to mix and master tracks than it was in previous decades.
I can find amazing techno tracks on Soundcloud and Beatport that are produced by some guy in his bedroom in Berlin that only a few hundred people in the world have also found.
Just the other day I found a track on Soundcloud that was produced in Melbourne back in 1997 that only ever had a single release of a few hundred CDs. I managed to track down the producer on Facebook and get a high quality .wav download of it. There's no way that kind of obscure stuff would've found its way to me pre-internet.
If you like that kind of music. There's absolutely no way in hell you will ever convince me that Kanye, or Daft Punk, have any, even most remote, relation to music, or art in general. Never heard the other ones, so I am not going to comment. And in the contemporary genres that I care about (adding contemporary, because really, Bach is better anyway, but I don't necessarily want to listen to classical all the time) it has been all downhill since the 70's.
All a matter of taste. There might have been a proliferation of genres, especially if you start enumerating all the (absolutely identical-sounding unless you are a trained maniac) varieties of Scandinavian Death Metal or electronic music, so it might be easier to come by something you like today, but it's not any better than what survived from 300 years ago, I would hazard a guess that very little, if any, of kanyes and deadmou5-es will survive even 10 years, let alone 300.
Many people wouldn't consider electronic music to be music or high brow. Many people are close minded.
Even within the electronic music scene, there's people that will dismiss genres as being not "real" music. A lot of people shit all over tech house for instance.
Not that anything needs to be high brow, but I do find GP's comment that there's more high quality music now than ever before to be rather closed-minded to begin with.
There may be more music (classifying, for a moment, anything that has that label as actually being music) made today, both due to the population increase and to it being easier and cheaper than ever to produce something and throw it to the masses, in case it sticks. But there's probably a lower proportion of quality music being made, for the same reason -- it's just to easy to make and disseminate stupid derivative junk.
It also might be that you have only now discovered that there is something better than beyonces and x-men movies. That doesn't mean that there weren't anything good before, just that you haven't seen it.