You're right that Garrett can't fix the defense and needs someone to come in and do that for him. That's where a lot of experience and a rolodex full of people you've worked with would be pretty useful. Since he got to skip the part of being a coach where you learn to do the job and build a resume, he really doesn't have a lot of connections to build a staff from. That's part of the reason it's hard to tell which hires are Jerry hires and which ones are Jason hires. We can't really draw lines from Jason to anyone else. Kiffin's tiny connection to Jason's cup of coffee in Tampa was as close as you were going to get to a "Jason Guy".
We need someone who, for once, can clean house here and bring in all of his own guys on both sides of the ball. A guy like David Shaw or Greg Roman maybe who could draw from Stanford and whoever isn't under contract in San Fran, with the added bonus that they come from a coaching tree that values the hell out of the OL.