You're right to an extent, but you have to remember that hip-hop is an artform based on sampling. Great producers don't just take a random sample, loop it, add drums and snares and call it a day, they chop it up and flip it. In the same vein, Jay doesn't take entire verses from rappers and pawn them off on his own. Rather, he's taken a bar here and a bar there. Plus, he's admitted that he does it to show respect to the greats that came before him. Whether you believe his rationalization or not is up to you, but he has admitted it. The man has undeniable lyircal talent when he's on the top of his game, so it's not as if those few random lines are reflective of his talent. I don't see why you view it as such a big deal, especially in the rap industry.