There are many aspects of humanity, and many different human qualities that hxh explores. Gon-san was the manifestation of of Gon's guilt and his internalized anger at his own weakness and failure. The little rose was an example, as the translations put it, of humanity's malice, specifically at that which is unknown and powerful. It represents humanity's unwillingness to surrender our power and control to something greater. However, it's also Meruem's humanity that allows him to adjust his world view and find something of value in humankind.
Gyro represents the used and the abused. The oppressed masses that have been forgotten and ignored. He's a shoe in for Meteor City. But he doesn't represent humanity itself, he's more a consequency of our neglect. He fulfills his role as a symbol for humanity for the ants who remembered him even if he's just a concept.
I know that was a bait post, but I feel it's worth saying.