DK is somewhat difficult and then sometimes he isnt. Pit's F-throw Chaingrab works well against DK, for one, maybe at least 3 F-throws if you are quick enough, maybe 4 or 5 Max before getting to the 40% line.
A DK that spams B-airs can be hard to approach because of the range, similar to a D3 spamming his B-air, without the Multiple jumps part. Shooting arrows at that point is one of your best options on that point.
DK does hate arrows just like many chars without Projectile defense do. An arrow can mess up a DK charging up his Punch.
You know about DK's grab thing, when he carries you? I still have that feeling to say "Let me go!" However, when he does carry you, hold the control stick either up or down to quickly break free of it without mashing buttons or beating up your controller. You can still press buttons while Holding the control stick Up or Down to further help you break free. Yes, I still have that "Let me go!" Feeling, because carrying a young angelic boy it makes him have fear
You can test it yourself and see the difference.
Pit's Mirror Shield works really well against DK's recovery, and since DK gots limited recovery options like Ike and Link, it's easy to guess when DK is going to use his recovery. Arrows are helpful in gimping DK or setting him up for a Mirror Shield reverse.
If you want to pursue him with F-airs, B-airs, or something, be careful not to get hit by F-air, D-air, U-air, or Side-B, and 3 of them moves are spikes.
Though Pit can combo a DK quite well, DK is very much a threat to Pit in terms of range. DK gots power and range in many of his moves. Because of this, I would not approach a DK from directly above. Gliding somewhat horizontally from DK's position is Okay, if the DK doesnt consider using his long ranged B-air. As C.F said, all smashes kill, and all of DK's spikes are lethal.
D-tilt can make Pit trip, and can set up trouble for us as well, especially with its range. In fact, let's just say that all of DK's moves got range, well, except the Side-B.
While DK's range and somewhat good speed (compared to other heavy chars) can trouble Pit, the fact that Pit can gimp DK really well with arrows, Mirror Shield, or even a chain of F-airs or B-airs (That doesn't happen that often to me) as well as being able to chaingrab the big ape really well gives Pit a decent advantage. But still, keep in mind of DK's great range advantage over Pit. This also discourages me from using Angel Ring against him.