I honestly can't wait till this fan base sees how defensively bad he is.
This is always such a weird criticism to me, because it's so ridiculously broad.
What part of his defensive game do you hate, specifically?
Is he weak in front of the net? Probably, he's like 20 years old and like 170 lbs. He's going to get pushed around by power forwards who are 6'3" 220 lbs but most players are going to get pushed around by those.
Does he make boneheaded plays while defending? Does he lose his man, get beat wide, let people walk to the net uncontested? Does he fail to block off lanes? Does he fold like a rented lawnchair under the slightest hint of a forecheck? Does he generally make poor decisions with the puck in the defensive zone?
When I watch Hughes play I don't see someone who is poor defensively. I see a young defenseman who gets overpowered occasionally, but has elite puck transition skills and fantastic poise who is most comfortable handling the puck under pressure. He has both elite skating and above average passing as options in his toolbox for evading a heavy forecheck and clearing the zone. He is prone to getting too fancy with his plays, but that will improve with maturity and time.
He is a little over-eager to jump up and join the rush which can sometimes blow up in his face and lead to an odd man rush the other way, but this is somewhat mitigated by his elite skating allowing him to come back and occasionally break up the play. I also think it's wrong to simply say something like "Hughes on average allows
3.8 odd man rushes against / 60 minutes due to his risky pinches in the offensive zone". I think you have to look at risk/reward and find a plus/minus of his risky plays. If he risky plays scores more goals for than they cause goals against, then it's a net positive.
I also think, again, that his decision making will improve with age. Right now he's feeling out what kind of risks he can get away with at the NHL level and I don't expect him to continue making the same poor pinch again and again and again. I expect him to become more selective and more effective at taking risks for offensive opportunities.
Hit shot will likely improve over time, but either way having a Phaneuf/Weber/Chara level heavy shot isn't required to be an elite offensive defenseman.