The NFL is a passing league, which means that rushing the passer is the top priority for any defense.
As important as defensive backs are, defenses can't be successful without a pass rush. Even if they have the best cover corners in the league, without a pass rush, it's just a matter of time before offenses pick them apart.
This is why the Packers have wisely placed a premium on acquiring edge defenders. Ever since Brian Gutekunst took over, he's made it a priority to acquire pass rushers with premium draft picks and top dollar free agents.