Superman's speech at the end is bizarre, and Robinson can't write Lois (or Jimmy, or Clark (without Rucka's help), or...) to save his life.
But to the attack...
Have you ever seen someone training a guard dog, or being trained to deal with a dog attack?
They wear thick pads, because even a well-trained, normally friendly dog, when it's in attack mode, is a vicious, dangerous weapon with fur. They will not only draw blood, they will rend flesh. Get the right breed, and they'll do a pretty good number on bone, too. Even a non-aggressive 'I'm hurt/sick/tired, just leave me be' nip from a smaller breed can draw blood (I speak from experience of being a kid who didn't realize the family dog had just gotten back from the vet).
So, no, Krypto's attack isn't particularly brutal, or 'rabid'-appearing. It's an actual, earnest attack, that's being portrayed relatively realistically.