“Easier” is an adjective. Is “easier” a good adverb? Is it easier to practice this way? “Easier” is a universal substitute for more easily. But if you try to use “easier” as a universal substitute for “someone more easily,” you end up sounding uneducated. In order for us to more easily perceive

that non-humans have agency,… or The addition of “That” is not absolutely necessary

but

makes the sentence flow better.

If a word isn’t the place of perception, the reader’s first instinct is to assume that we are “non humans” is the object of perception. Does this not the case becomes clear pretty quickly, but the addition of “that” ensures that the confusion does not occur in the first place.