Stability matters, but you're ignoring California's actual defensive production last year. They ranked 102nd nationally in yards per play allowed at 6.1. That's not a foundation, it's a liability. Miami's defense, even with roster movement, finished 22nd in defensive SP+ and returns a core that generated 31 sacks. The "proven structure" you praise gave up 34 points per game in conference play. Meanwhile, Miami's defensive success rate was top 25, and that's with integrating new pieces which is the modern reality. You can't exploit a gap if your system hasn't proven it can stop anyone.