As far as I'm concerned, Jay didn't bring anything new to the table. He's a good lyricist, actually damned good, but that's it. He rode Jaz's coattails for years and snuck in behind Biggie basically spittin about the same shit. If Big was still alive we'd likely be talking about Jay in the same breath as AZ; a cat with lyrical skill but trying to do the same shit that Biggie and Nas were already doing but better.
Nosign.
Aside from being a top tier lyricist (not necessarily the absolute best) Jay has one thing that AZ doesn't have:
The ability to make a hit song.
2Pac and Biggie both had that skill (or maybe it was 2Pac & Biggie's management team/A&R). Whoever it was knew how to make a hit. There's a difference between a dope song and a hit. One of my favorite songs is Purple by Nas. The beat is smooth and his lyrics are fire, but it's not a hit. A hit has that "X" factor. There's something about the song that people find catchy. When you play it at a club or a party it makes people gravitate towards the dance floor. You know how when you're at a party and the dance floor is empty and the DJ throws on that song and EVERYBODY rushes to the dance floor and the dance floor is packed 20 seconds after the song starts?
There's a lot of top tier lyricists that could go bar for bar with Big, Jay, Nas but they can't make a hit single if their career depended on it (see what I did there). In fact Nas himself was in a slump circa 2000. He couldn't put together a hit song. His beef with Jay saved his career. He couldn't make a hit song, but he could write a battle rap.
I don't know if it's Jay Z or his management team/A&R that makes the hits, but he's lasted 20+ years after Pac and Big's death and remained relevant. It's foolish to say, "the only reason Jay got on is because Big and Pac died". That statement made sense in 97/98/99. But it's 2019 and he's still one of the top 5 most relevant MCs in Hip Hop. The Story Of OJ wasn't a hit in the traditional sense, but it got play and I'm sure everybody has heard it by this point.
I have to reject the notion that the only reason Jay got on is because Pac and Big died. I'll admit there was a void, but it's been 20+ years and he's still on top. Pac and Big's death has nothing to do with his longevity.