Plural champions, no plural hearts, plural children taken together, because literally all life on azeroth would be taken if azeroth were to die.
that does not mean every living creature on azeroth has a heart of azeroth.
multiple people can make 1 thing.
and if there was 1 per person, why would it mention 1 thing being made by multiple people, and not 1 made by 1 person, that way each person has their own?
So lets compare it
We have a chair.
A symbol of comfort
made by the people in shop class.
That does not imply every single person made their own chair, that implies every single person worked together to make A CHAIR.
if it was plural it would be
A symbol of comfort
Each made by the people in shop class.
or
A symbol of comfort, Made by each of the people in shop class.
It lists singular item, plural creators, no where does it imply multiple items, only multiple people, it lists a singular item.