We have to work on both simultaneously.
If the secondary is too weak the QB can throw the ball up knowing we can't defend it no matter how good our passrush is.
We don't need a great secondary, just an above average one so long as we can accompany it with a good pass rush.
I wouldn't hesitate to take the CB if he is the better player than reach on an OLB/DE who may be a bust. That is how you build a decent team.
For all the hubbub of the Giants and their investments on the DL they also gave Rolle a big contract, Kenny Phillips was a 1st round pick, Aaron Ross was a 2nd round pick and Corey Webster was a 2nd round pick.
The Giants just do a better job of not wasting cap money on overpriced vets so they can compete in FA for players. They also do a better job of not whiffing in the draft as much as us so they have reasonable depth via the draft and UDFA.
We can get better but Jerry has to manage the cap better. He needs to get core players extended earlier in their careers for more reasonable deals and he has to let declining vets to somewhere else while we bring in young kids in FA even if it means paying them a bit of a premium. The Rat and Witten extensions were a step in the wrong direction, IMO. The Oscan signing was a step in the right direction but they just overpaid way too much given that he had never earned a starting spot.