I agree with you for the most part, but I don't think its as black and white as you say. Yes could we improve consistent pressure with our DL? Sure. But pure talent alone, our secondary room is possibly bottom 10 in the league. We are in desperate need of playmakers in the secondary.
Even if we play zone, a playmaker in the secondary makes QBs double take and 2nd guess throws, which in turn will help our pass rush.
Also, Quinyon Mitchell played mostly zone in college, had 6 INTs in the last 2 years.