Heres how you can give the Kent's a decent arc of their own.
They find Kal-El in the field. Decide to leave him in an orphange, but they have become attached to him, and legally adopt him.
Years later. The Kent's have raised Clark as the best kid they could. This could evolve into a nice debate between Jonathan and Martha about wether or not they raised Clark to always say and do the right thing, out of fear. That he only cares so much because thats what the Kent's raised him to be like, in case he ever thinks of himself to be superior. Of course we know that even if the Kent's had a son of their own, he would still be like Clark, because they raised him out of love, not fear. I know thats never been in the comics, but its a realistic question they would ask themselves. Just doubting themselves as decent parents
Then when Clark starts prepairing to become Superman, they initially support him, but express their fears and concerns of wether the world will accept or fear him, and if things dont work out, he could come back to the Farm. Then Clark reminds them that they shouldn't doubt themselves in any way, because they adopted and raised him out of love, not fear. If they cant accept him, then he will try to make the world understand