There's really not a whole lot there.
After jumping from place to place as a position coach (mostly WRs or DBs) for the first twelve years of his career, he landed an NFL gig with the Vikings from 2007 to 2009. Get this, as the assistant DB coach. I didn't even know there were assistant position coaches, heh.
But then his claim to fame arrived: was hired by Jim Harbaugh at Stanford, and stayed on through the Harbaugh to David Shaw transition. While working for Shaw, rose from DB coach to Assistant DC, and then to Defensive Coordinator and Assistant Head Coach.
These were the years when Stanford was really good, including PAC conference champs a couple of times. And one of those years, Mason was picked as a finalist for the Broyles Award (best assistant coach in college football). He didn't win it, but was a finalist.
So folks thought well of him. Well enough for Vandy to give him a shot at head coach. Where the Peter Principle kicked in, and he finally got kicked out. I mean, he became the first and only coach in Vandy history to go winless throughout a season. You'd think it would have been done prior, but nope, he was the first. Ouch.
Since then, he has had a couple of one-year tries at DC again: Auburn in 2021, and Oklahoma State in 2022. Neither panned out.
So yeah, I'm not sure why everyone thinks he would be such a ****-hot DC. I guess they're enamored of his Stanford years.
Go Vols!