JJ is a better player, but Cushing position has a lot more impact. DE just isn't a huge impact position
Which makes Watt exponentially more valuable, because he brings so much out of a position that historically doesnt do much.
It very much is. It's one of the positions that teams are willing to spend a #1 pick on, outside of LT and QB. Usually if a defensive player is going #1 in the NFL draft, it's a defensive linemen. So it is a pretty huge position. I think people think Cushing has more impact because Watt hasn't missed much time (if any at all?) and hopefully it stays that way.
Actually, our defense started to really look bad when Joseph stopped being pro bowl caliber. Cushing played in our debacle against GB. And he didn't play against our destruction of the Ravens the following week. So really it should be about Joseph being the best defender by your logic. But I'll ask you this question. Suppose Cushing is removed from this team, would you trade Watt for Patrick Willis? I'll even lessen Willis' contract to be on par with Watt's for the sake of fairness.