10M per year for a SB-winning coach? Sure, that makes sense to me. Honestly, if you aren't willing to bet that your coach is worth $10M you probably shouldn't be hiring him in the first place.
But... giving a 10 year deal to a guy who hasn't coached in basically a decade? That's ****ing insanity. What happens if 4 years from now they haven't made meaningful progress and it becomes quickly apparent the game has passed Gruden by in the decade he's been away? You can't very well fire the guy, unless you're willing to eat $60M while he retires, which by the way is over 10% of Mark Davis' net worth.