Legion-5 didn't let up after he assimilated Legion-7 and the dragon heart. He can use the dragon heart now but that is not enough for him. Legion-7 and the dragon heart have to fuse. It is only then can he successfully create a synergistic effect between the two divine abilities that amplifies the power of both of them.
Legion-7 spoke. "I guess it is my turn now."
"Let's see what I can do first before you get to work."
Legion-5 tried the effect of the heart first. His hand became scaled and clawed. Blue lightning flickered playfully in the palm of his hand. This is something that only Supreme beasts can do. Other races that fuse with a dragon heart can not bring it back to life and use the element that the original dragon could use while it was alive.
"It is not bad. But it is not enough. You can get to work now."