It's a toss up and when you throw in what they're actually capable of and the things they withstand, they really have no means of truly hurting each other. A "bullet" holds no significant weight, armor or not, when our tanks are shrugging off mega sky laser death beams and literal mountains thrusted upon them. Even taking that out of consideration, if they were brittle and mortal like us for whatever reason, being sliced in half by a giant metal sword is about as fatal as being shot in the head by a bullet.
It really just comes down to "my favourite class" will win and you can make up any reasonable argument for it.
A coin to DRK is that despite their heavy armor and giant sword, they don't truly move significantly slower than a GNB. If anyone has played DRK, they would realize they are capable of bursts of immense speed *whilst* holding a slab of metal as tall as them. See old Blood Weapon/DRK being the OG double weave oGCD tank class/ etc.
By animations you can argue that GNB swings more times than DRK but it's an argument of multiple moderate 1h Slashes versus a single giant heavy 2h slash. Explosion vibration versus d A r K n e S s for effectiveness is not realistically measurable.
And despite GNBs trenchcoat, they do notably wear body armor underneath it which is likely to be as or even more durable than DRK's armor, depending on the material. Likewise for DRK with it's armor and theoretical material.