One thing that's interesting about this, and I've thought about this a lot, is that you can clearly see the Oilers were targeting the Canucks right side defence for zone entries. The exception is Burroughs. So the Oilers are consistently trying to enter on the weaker partner. Hughes, OEL, and Burroughs with single digit zone entry attempts against while Schenn, Poolman, and Stillman with double digits. Apart from Poolman, the strategy didn't actually work out that great. They should have targeted Hughes rather than Schenn.
This is kinda the problem with Hughes. As dynamic as he is offensively, he's got his shortcomings defensively that i'm not sure he'll ever really completely overcome. He's challenged in denying/containing zone entries. He just doesn't have the reach or physicality to dictate anything. But attacking the other side is also a viable strategy when that side is so weak, in terms of setting a tone. If you decide you want to make a statement, you don't mind attacking the other side and forcing Hughes to be the one going back to retrieve pucks. Just opens up those opportunities to get in an try to rattle him with a physical forecheck.
If he's your "top defenceman" playing "big minutes", other teams have to worry a little bit about his counterattacking ability, but by and large, it can make things just a little too easy to play against. Where a team can kind of be content to attack him directly for entries, or just force him to keep going back to fight for possession and keep having to try to break the puck out. Either way, potentially putting the team on it's back foot trying to regroup for a lot of the game. And it doesn't necessarily take "top skill players" to pressure his pairing into playing on that back foot. Even just run of the middle speedy grinders can make life more difficult for Hughes and the forwards playing with him, by disrupting and retreating. Even ugly chip 'n chase hockey can be effective in forcing a bunch of energy expenditure.
Just tough to "anchor" a blueline around a guy like Hughes. In the same way the contending Canucks of yore couldn't really "anchor" their blueline around Ehrhoff. Getting a better partner for Hughes would certainly go a long ways in mitigating some of that issue...but at the end of the day, you're still always going to want to be trying to take control of his minutes/deployment. Unlike your archetype "all around Stud #1D" where you can dictate the matchup game the other way with teams wanting to get their skill players away from them.
It is what it is. Hughes in a fantastic offensive defenceman. It just comes with limitations as your #1.