Questionable math asides.... The “7/1” is a guide on how we biologically age. It equates to stages of biological development. It’s not the actual “age” of the animal nor is it how they perceive time. In fact- “7/1” is more a general tool, but that ratio changes depending on the dogs breed and age. Small dogs can easily live 15 years, which would make them 112 human years Very large breeds may only live 7 years, and medium large dogs live about 10 in general. The oldest dog on record was 29- 203 human years if we use a set literal7/1. As puppies you can also see it doesn’t hold up well since a puppy grows very quickly and can reach sexual maturity in 6-12 months- by 7/1 that would be a 3-7 year old child capable of raising babies. In truth we have little solid facts on how other animals perceive time, however there is evidence that suggests smaller creatures perceive things moving slower than larger ones. To get to “bullet time” though you'd likely need to be insect sized if that’s true
They don’t “need” to exist- it’s human need that causes them to exist. Humans like to, really need to (to some extent) view the world trough a human lens. The human perspective and condition are not just the only thing we know, but they are our only intuitive reference. As such humans anthropomorphize inanimate objects, shadows, we can bond with even just a sound so long as we find familiarity. Dogs are intelligent, feeling creatures that have evolved not just besides us, but we have both co evolved to compliment each other. So most of all one might say many humans seek to find the familiar- the “human” in dogs. “Dog years” are just a tool by which we relate the dissimilar development and life cycle of dogs to humans. It fills an emotional need for some, as well as making it easier to relate general information about the dog in a way we can quickly understand. It is not correct but mostly works in a practical sense- a 10yo dog is old, so is a 70yo human. We get what that means.
I feel like nobody would be confused without them.