It's certainly a glaring need in terms of the position not being filled (none of us want to see Jack Crawford get significant snaps), but it's not nearly the same need in terms of roster and draft value.
A 3rd/nickel CB is going to play a lot more snaps, and a bad player in that position is going to be a much bigger liability than a DE who could end up playing only about 30% or fewer of the defensive snaps. We're much shallower at that position than anywhere else, and it's easily our biggest hole.
A lot of our nickel packages last year included Casey and Simmons as the only two DL's on the field, or even just 1 of them, with Evans coming down to the line sometimes, and Landry/Correa (and Roberson in the playoffs) coming off the edges.
And I'm actually OK with Jones playing more snaps in Casey's place as a run stuffer in a nickel set, where we're smaller everywhere else. He's always graded pretty well and is just a solid player. There's no one in the draft where we are that jumps up as someone who's game changing interior DL.
Now obviously, if we could get Clowney that would change everything. He could play either DE in base sets, then keep him and Simmons on the field in Nickel/Dime sets and move him all over the place as a chess peice. But as for the draft, there's other positions with far more value as far as the quality of prospects in the back end of the 1st.