While I don't necessarily disagree with anything Raziek has said, he doesn't really touch on how Duck Hunt may be able to capitalize the MU.
Duck Hunt and Robin are all about controlling the stage and engaging when their traps are sprung. Robin is really only good at that with Arcfire and Arcthunder, and Arcthunder is stuffed by all three of DH's projectiles; Elthunder hits too quickly for Robin to follow up out of it. Gunman is really good for pressuring Robin particularly because he can tank Arcfire (and even counterattack if the gunman in particular is fast enough), allowing for DH to escape, and a Gunman plus a Can plus yourself is a great combination to make sure they can't just sit still and charge Thunder.
We'd much rather fight Robin in the air, mostly because we have an easier time controlling airspace than she does. By which I mean: while her aerials are strong and sweeping, covering huge areas around her, the Can allows for forcing an option and capitalizing on that, and she has no particularly safe long-range aerial game like we do. Her airspeed is decent, and Elwind is a great panic option, but it's not enough to escape our equal-if-not-better airspeed and our own disjoint if we can force something out of her.
Duck Hunt is hardly afraid to box: our jabs both come out on frame 4, although hers is more disjointed, being a sword. Our ftilt and dtilt are great pokes with great disjoint, and our utilt is useful in that it's a move as opposed to Robin's limp noodle swing. While Duck Hunt has no kill throws or guarantees, he has 0-to-40 throw setups, and unlike Robin, Duck Hunt is a Jedi when it comes to grab range. Like Raziek said, the Can is our only real defense option if she's juggling us, but that's a whole lot better than most characters can say anyway: I'd rather take 8% from my own Can than another 24% from two Levin fairs.
And I'd argue that Duck Hunt's on-stage edgeguarding is about as good, if not better than Robin's. While it's true that Arcfire covers most options/Duck Hunt has no options on the ledge, it's a perfectly valid option to just stay on the ledge and let it burn out and then react to what comes next, or to try and evade it by dropping down and grabbing it again (particularly since, if Robin is spacing Arcfire correctly, she won't have the run speed to punish our regrab before we can buffer a roll or something, and if she goes ham with a dair or something and it doesn't pay off, now she's offstage instead).
Duck Hunt, however, has the whole package: a correctly-spaced Can will force an option, because the alternative is to hang there and take it. Can covers the jump and the nothing; Disc covers the get-up and the roll; Gunman covers the attack and the roll; and Duck Hunt covers everything. Of course, it's not very likely that you'll have all three projectiles out and ready to cover everything, but my point is, his pressuring game is SSS+ tier.
Offstage, yeah, Duck Hunt is gonna get bodied. Your best hope is to throw out a Can and try to recover with it: even if you have to take the extra 8%, it's at least not likely that you'll die from it. Up B actually has a fair amount of distance to it, so otherwise your hope is to try and juke Robin by fading away or something, but don't expect miracles.
All this said, Raz was right that it's going to come down to who gets the kill first. Duck Hunt has a slight edge in the neutral game, but Robin's own projectiles, her lingering hitboxes, and with how quickly her aerial kill moves come out, make approaching with our own kill moves a nightmare. Her ****ty run speed doesn't mean jack when our smash attacks, as strong as they are, aren't safe on shield (and remember, at 90% she only needs one grab) and can fail on hit because of reasons. We have no guarantees out of throws. Our best options are to pressure a response and capitalize, or to keep throwing Cans until it kills eventually. Our offstage game isn't even all that impressive: our hitboxes are too precise to track Robin's sweeping momentum with Elwind, save for nair, and if you don't sweetspot nair, you're really only making things harder on yourself (unless she just so happens to run out of Elwind).
I don't know about -1.4 or whatever, but it's at least a -1 for Duck Hunt. We both specialize in pressure and traps; Duck Hunt is a little better at racking up damage; Robin is a lot better at killing.