I dunno, I know we are getting into "how hot is the sun compared to a nuke" territory, and "how deep in the sun can they go" and "how hot did Robert Kirkman think the sun is," but... A heat based attack taking out a guy who fights in the sun and gets caught in the blast wave of an exploding planet just doesn't sit right.
Maybe slicing that chunk of the planet is really that much more powerful than continued presence in the sun, I dunno.