Well, this was HF said about him:
Talent Analysis
Coburn is a mostly stay at home defenseman who skates very well and makes a good outlet pass. Though not a bruiser, he uses his size to his advantage.
Future
Coburn is still loaded with all the right raw materials and his potential remains extremely high. But neither offensively gifted nor a physical force, Coburn’s career hinges on him being very solidly defensively, and that’s where he needs to improve.
Personally I've never seen any real offensive instincts from Coburn. He makes a decent pass, and when he's set up he can crank a hard shot, but he doesn't doesn't create much of anything offensively.
I think that analysis was spot on, he has become elite defensively but not much more than that.