Being entirely reactionary = bad.
DK ultimately takes a risk in this matchup more than ROB because he HAS to approach. ANYTHING he does that ROB knows how react to can and WILL be punished. The key thing I should point out though is that ROB doesn't have to react to anything to force DK to approach. When he shoots a laser, he is able to deal damage from a distance, and DK does not have a way to deal damage from that distance.
The only time DK has a low risk situation to KO someone is from a headbutt combo, but there is significant risk trying to actually land the headbutt (don't believe me? Check your frame data, and it's MUCH easier to punish stuff out of shield in real life matches, which I don't do as effectively online), which is a more situational and punishable attack than the Giant Punch, minus the fact it doesn't need to be charged. Granted, this makes ROB need to think twice before shieldgrabbing, but ROB has more than one way to punish DK's approaches and DOES have enough time in between attacks to do something out of shield.
A DK that properly spaces is more easily punished than other high level characters that properly space. In order for DK to be perfectly spaced, he needs to keep his hurtbox AND his hitboxes away from attacks in risky situations, and he needs to avoid any projectiles that the opponent may have, not to mention he must keep the opponent away from his blind spots in front of him and below him, which are worse than the blindspots ROB has below and behind him. Other characters, they properly space, you attack their hitboxes, and end up getting hurt in the process. Or they just stay away from you and are able to hit you.
Yes this is theory talk, but you should keep in mind people have not been developing strategies for countering DK as long as they have for someone like....Snake. Snake was CLEARLY a broken character when Brawl came out. Most people thought DK sucked for a long time before Riot won a 60 man tourney (yeah, skler's guide to Link still says DK is worse than Link). Yes, people have been spending a lot more time countering the sacred 7 than they have countering DK, who I understand is doing decently right now.
All in all, I think you overestimate DK. I feel the main reason he's doing well right now is because he's a lesser used character than most, and not considered a "real" threat due to DDD's infinite chaingrab on him. See, I don't hear anyone saying DK has any "broken" defensive techniques. And for a good reason cause other characters have more broken stuff to use, and yet THOSE things are being countered in various ways as we speak. Snake's F-tilt for example can be punished on its ending lag. G&W's Back air can be Up-Bed out of shield easily by a few characters. Metaknight's Tornado can be countered with all sorts of dumb stuff and can be DIed out of easily by lightweights. These are examples of techniques that are CLEARLY more broken than stuff DK has, and you expect your stuff to stay not countered forever when in reality DK clearly isn't a character who is always able to force the game on his terms?