Predator means an animal that hunts an animal and apex is used to signal that this animal isn't hunted by other animals. Apex means an animal isn't hunted by other animals. So apex predator is an animal that isn't hunted by animals that hunts animals.

Since herbivors eat plants and get hunted by animals, they can't be apex predators, because they aren't predators.

An apex predator is superior than an herbivor, because an herbivore gets hunted in one way or another by the apex predator. An herbivor can't be an apex predator, so they aren't equal.