Quoting: CD282
Dumba and Dunn aren't good defensively - you have both players playing above their established ability defensively.
That's just categorically false. If Dumba were strictly a #4 defenseman who couldn't play any higher, then yes you'd be right. Unfortunately for you, Dumba is most definitely a top 4 defenseman and more than capable of handling a top pairing role, duties and minutes, and has done so at numerous times throughout his career with the Wild.
The caveat in this trade, isn't whether Dumba can play in a top pairing role, as he can. It's if Edmonton can properly support him with a defenseman who can hold the zone defensively while Dumba counter attacks off the rush.
Edmonton's best defensive d-man is Bear, but he plays the same position. So he's out.
Nurse is by far the best choice here because he plays a decent two-way game, even if he’s more inclined to offense than defense. The catch here is Nurse willing to be more of a stay-at-home defenseman if he’s paired with Dumba?
Simply put, Dumba to the Oilers doesn't work not because he can't play the part but because the Oilers defense suck on actual defense. That's more of a Oilers problem then a Dumba isn't good enough to play up there problem.