SJ was a great defender in the halfcourt cuz he could see the screen & roll with them — perhaps better than any defender I've witnessed in my 30+ years of following BYU hoops.
But SJ DID at least pass his skill on to Richie & Knell (not that they're as masterful as he was).
As an overall defender, though, SJ was pretty limited. Mag is an extremely valuable guy for breaking switches. But also for getting out in the front in transition. Both as a runner & as a defender. If you hadn't noticed, he's extremely fast.