Gruden had a loooooong run of mediocrity after the superbowl win. I'm not wild about his chances with the Raiders, but I can see this trade better from the Raiders perspective than the Bears. Mack is a great player, but would you rather have 25 million in cap space and 2 future firsts from a team that will, IMO, be lousy... or Mack?
The only position I think worth going bonkers financially with is QB, after QB your roster needs balance. I don't think the Raiders were winning a superbowl in the next few years with Mack, but locking him into that contract should would have made adjusting their roster difficult.
The Bears on the other hand... I really don't get it from their end. They have a LOT of holes. They're not a star defender away from contention. Even if Trubisky is a stud, and that is a big if, he needs weapons... a line, their defense has plenty of holes. I just don't get it for them. Unless Mack goes out there and injures Rogers and 5 Vikings, I don't see the profit for them.