Jay hasn't been trash. He has versatility, wit, great production, and an overall ability to navigate records, over Nas. I wasn't feeling Blueprint 3 very much, but American Gangster was

from top to bottom, and he actually performed really well on Watch The Throne, showcasing different sides of himself topically and introspectively. And even Blueprint 3 had some heaters.
I think Nas being the "superior talent" is debatable, but what's just as debatable is Jay-Z having the superior catalog, because in my opinion, he seems much more efficient at putting everything together than Nas is

.
Nas is incredible, too. I think he's the more candid storyteller and scene-setter between them, and even though I think his flow is better than Jay-Z's, I don't think Jay's flow is garbage. But just about everyone - himself included - acknowledges that his production isn't as consistently good as it should be, and that he's had many of his share of faulty attempts at making the types of songs that he isn't good at making.
A lot of people get so caught up in what they feel Jay-Z represents - commercialism - that they let it blind them from how dope he really is. By contrast, a lot of people get so caught up in what they feel Nas *does* represent - "real hip-hop" - that they overlook his faults.
What I don't get is why people always feel like they have to choose between the two of them. Jay-Z and Nas are both Top 5 emcees, IMO. The beef was years ago, and it doesn't have to dictate one being good and one being bad.