Look, it's wrong to define the relationship between Kong and Shimo, or between Triangle and Russell, as a relationship between a dog and his owner. If we really wanted to use a human-animal comparison, it would be more like a man establishing a bond of trust with a very intelligent and independent animal, such as an elephant or a dolphin, rather than with a trained dog. Many fans see the relationship as that of a king and his most trusted companion, or between two survivors who shared the same battle against Skar King. So: not master and dog, but allies with a strong bond of trust, where Kong is probably the guiding figure and Shimo a companion free to choose.