Firstly, a minor point: Wayne's dominant era is already a decade ago, and he is of the older generation of rappers now.
Wayne is not a "deep" rapper most times (although he has his moments, e.g. Tie My Hands and I Feel Like Dying). He's a punchline rapper - one who isn't trying to convey Meaning but just have fun on a beat. This tradition has a long history in hip-hop, going all the way back to the Sugarhill Gang and "Rapper's Delight".
His mixtape work is widely acclaimed as classic stuff - Da Drought 3, Dedication 2 and No Ceilings being the most prominent. His music has endless quotables, e.g. "real G's move in silence like lasagna"[0]. Rap heavyweights like Ice Cube, Eminem, Busta Rhymes, Kendrick Lamar, Nas and Raekwon have high opinions of his work, with hip-hop pioneer KRS-One calling him the "greatest rapper of all time[1]." Post-Wayne rappers betray a huge influence, with e.g. Kendrick Lamar, Young Thug, A$AP Rocky, and most prominently Drake.
You had opera and musicals long before MTV and Youtube. And people mostly didn't hide their faces during live performances before or during the current period of recorded music.
Nobody cares what the pianist looks like :)
To be fair: Taylor Swift and Beyonce - if you see them totally without makeup, are not super attractive, they look in the range of fairly normal. Also there's a double standard for men and women to some extent. Top male artist right now is Ed Sheeran and he is one ugly mofo, then again, to my point - he's highly talented ... when he's not writing pop tunes 'designed for a mass audience' he does some cool stuff. On Charlie Rose he basically admitted he writes a lot of stuff for commercial purposes, it's a business.
There are many very objective metrics we can use, but even by many creative metrics - it's worse.
Lyrically: have you ever listened to what 2Pac or Biggie were saying? They were rhyming. There was an obvious lyrical flow. Now compare to Lil' Wayne who literally spouts gibberish. Lil wayne 'says words' to 'a beat' and that's it.
Some people point out that 'there's always been bad music' i.e. if you go back to the top 40 in 1977 or whatever it's litered with derivative crap - but - there were many 'stand outs' of great music - even great pop music. For example, Michael Jackson was not exactly an exalted artist in the purest sense, but he was a genius pop artists. I fully respect Beyonce as a hard working and creative entertainer of our times, but I think in 10 years from now, you'll more likely hear a Michael Jackson song than a Beyonce song.
Underlying issues are partly commercialization, but also - 'visualization'. Remember 'video killed the radio star?' - well YouTube is the new MTV and 'how it looks' is as important than 'how it sounds'. Pop stars now generally are more attractive.
Also - it's just too easy to press a button and make noise - people confuse the creativity behind that with raw expression. I saw a band recently that had 2 guys playing 'a computer' and it was interesting, but ultimately very empty. The lack of character has me aching for good, live Jazz. :)
I love Kanye, but it's really hard to get fully behind someone standing there with a microphone, it's like a big Kareoke show.