You draft the right QB for the right system. These days you don't "develop" a QB. You either drafted him or, you didn't.
Andrew Luck, Russell Wilson, Tom Brady, Matt Ryan, Dak Prescott, Ben Roethlisberger, Cam Newton, Joe Flacco, Marcus Mariota, Jameis Winston, Derek Carr, Drew Brees, are some names who were never "developed" to be the starting QB. They either took it over at training camp or were thrown into the fire because of an injury.
Not really rocket science. We're still waiting to draft the right QB, you don't "develop" one